The Futuristic Gun Duel

Question

The Background Future

In the year 2017, you and your opponent will face off in a futuristic gun battle where only one may survive. Are you experienced enough to defeat your opponent? Now is the time to polish your guns skills in your favorite programming language and fight against all odds!

Tournament Results

This tournament ended on the UTC morning of Feburary 2^nd, 2017. Thanks to our contestants, we have had an exciting futuristic tournament!

MontePlayer is the final winner after a close battles with CBetaPlayer and StudiousPlayer. The three top guen duelers have taken a commemorative photograph:

                MontePlayer                         - by TheNumberOne
              +------------+
  CBetaPlayer |            |                        - by George V. Williams
 +------------+    #  1    | StudiousPlayer         - by H Walters
 |                         +----------------+
 |    #  2                        #  3      |       
 +------------------------------------------+
    The Futurustic Gun Duel @ PPCG.SE 2017

Congratulations to the winners! Detailed leaderboard is seen near the end of this post.

General Guidance

• Visit the official repository for the source code used in this tournament.
• C++ entries: please inherit the Player class.
• Non C++ entries: select one interface in section Interface for Non-C++ submissions.
• Currently allowed non C++ languages: Python 3, Java.

---

The Duel

• Each player starts with an unloaded gun that can load an infinite amount of ammo.
• Each turn, players will simultaneously choose from one of the following actions:
  • 0 -- Load 1 ammo into the gun.
  • 1 -- Fire a bullet at the opponent; costs 1 loaded ammo.
  • 2 -- Fire a plasma beam at the opponent; costs 2 loaded ammo.
  • - -- Defend incoming bullet using a metal shield.
  • = -- Defend incoming plasma beam using a thermal deflector.
• If both players survive after the 100^th turn, they both exhaust to death, which results in a draw.

A player loses the gun duel if they

• Did NOT use the metal shield to defend an incoming bullet.
• Did NOT use the thermal deflector to defend an incoming plasma.
• Fire a gun without loading enough ammo, in which their gun will self-explode and kill the owner.

Caveats

According to the Manual for Futuristic Gun Owners:

• A metal shield CANNOT defend from incoming plasma beam. Likewise, a thermal deflector CANNOT defend from incoming bullet.
• Plasma beam overpowers the bullet (because the former requires more loaded ammo). Therefore, if a player fires a plasma beam at the opponent who fires a bullet in the same turn, the opponent is killed.
• If both players fire a bullet at each other in the same turn, the bullets cancel out and both players survive. Likewise, if both players fire a plasma beam at each other in the same turn, both players survive.

It's also noteworthy that:

• You will NOT know your opponent's action in a turn until it ends.
• Deflecting plasma beams and shielding bullets will NOT harm your opponent.

Therefore, there are a total of 25 valid action combinations each turn:

+-------------+---------------------------------------------+
|   Outcome   |               P L A Y E R   B               |
|    Table    +--------+-----------------+------------------+
| for Players | Load   | Bullet   Plasma | Metal    Thermal |
+---+---------+--------+--------+--------+--------+---------+
| P | Load    |        | B wins | B wins |        |         |
| L +---------+--------+--------+--------+--------+---------+
| A | Bullet  | A wins |        | B wins |        | A wins  |
| Y |         +--------+--------+--------+--------+---------+
| E | Plasma  | A wins | A wins |        | A wins |         |
| R +---------+--------+--------+--------+--------+---------+
|   | Metal   |        |        | B wins |        |         |
|   |         +--------+--------+--------+--------+---------+
| A | Thermal |        | B wins |        |        |         |
+---+---------+--------+--------+---------------------------+

Note: Blank cells indicate that both players survive to the next turn.

Example Duel

Here's a duel I once had with a friend. Back then, we didn't know much about programming, so we used hand gestures and signalled at the speed of two turns per second. From left to right, our actions were in turn:

    Me: 001-000-1201101001----2
Friend: 00-10-=1-==--0100-1---1

As per the rules above, I lost. Do you see why? It's because I fired the final plasma beam when I had only 1 loaded ammo, causing my gun to explode.

---

The C++ Player

You, as a civilized futuristic programmer, won't directly handle the guns. Instead, you code a Player that fights against others'. By publicly inheriting the c++ class in the GitHub project, you can start writing your urban legend.

Player.hpp can be found in Tournament\Player.hpp
An example of a derived class can be found in Tournament\CustomPlayer.hpp

What you must or can do

• You must inherit Player class through public inheritance and declare your class final.
• You must override Player::fight, which returns a valid Player::Action every time it is called.
• Optionally, override Player::perceive and Player::declared to keep an eye on your opponent's actions and keep track of your victories.
• Optionally, use private static members and methods in your derived class to perform more complex calculations.
• Optionally, use other C++ standard libraries.

What you must NOT do

• You must NOT use any direct method to recognize your opponent other than the given opponent identifier, which is shuffled at the beginning of each tournament. You're only allowed to guess who a player is through their game-play within a tournament.
• You must NOT override any methods in Player class that is not declared virtual.
• You must NOT declare or initialize anything in the global scope.
• Since the debut of (now disqualified) BlackHatPlayer, players are NOT allowed to peek at or modify the state of your opponent.

An example duel

The process of a gun duel is performed using the GunDuel class. For an example fight, see the Source.cpp in section Initiating a duel.

We showcase GunClubPlayer, HumanPlayer and the GunDuel class, which can be found in the Tournament\ directory of the repository.

In each duel, GunClubPlayer will load a bullet; fire it; rinse and repeat. During every turn, HumanPlayer will prompt you for an action to play against your opponent. Your keyboard controls are the characters 0, 1, 2, - and =. On Windows, you can use HumanPlayer to debug your submission.

Initiating a duel

This is how you can debug your player through console.

// Source.cpp
// An example duel between a HumanPlayer and GunClubPlayer.

#include "HumanPlayer.hpp"
#include "GunClubPlayer.hpp"
#include "GunDuel.hpp"

int main()
{
    // Total number of turns per duel.
    size_t duelLength = 100;

    // Player identifier 1: HumanPlayer.
    HumanPlayer human(2);
    // Player identifier 2: GunClubPlayer.
    GunClubPlayer gunClub(1);

    // Prepares a duel.
    GunDuel duel(human, gunClub, duelLength);
    // Start a duel.
    duel.fight();
}

Example Games

The least amount of turns you need to defeat GunClubPlayer is 3. Here's the replay from playing 0-1 against GunClubPlayer. The number in the paranthesis is the number of loaded ammo for each player when the turn ends.

 :: Turn 0
    You [0/12/-=] >> [0] load ammo (1 ammo)
    Opponent selects [0] load ammo (1 ammo)
 :: Turn 1
    You [0/12/-=] >> [-] defend using metal shield (1 ammo)
    Opponent selects [1] fire a bullet (0 ammo)
 :: Turn 2
    You [0/12/-=] >> [1] fire a bullet (0 ammo)
    Opponent selects [0] load ammo (1 ammo)
 :: You won after 3 turns!
 :: Replay
    YOU 0-1
    FOE 010
Press any key to continue . . .

The quickest way to be defeated by GunClubPlayer without making invalid moves is the sequence 0=, because the bullet shoots right through the thermal deflector. The replay is

 :: Turn 0
    You [0/12/-=] >> [0] load ammo (1 ammo)
    Opponent selects [0] load ammo (1 ammo)
 :: Turn 1
    You [0/12/-=] >> [=] defend using thermal deflector (1 ammo)
    Opponent selects [1] fire a bullet (0 ammo)
 :: You lost after 2 turns!
 :: Replay
    YOU 0=
    FOE 01
Press any key to continue . . .

---

The Tournament

The tournament follows the "Last Player Standing" format. In a tournament, all valid submissions (including the GunClubPlayer) are placed in a pool. Each submission is assigned a randomized yet unique identifier that will stay the same during the whole tournament. During each round:

• Each submission begins with 0 points and will play 100 duels against every other submission.
• Each victorious duel will grant 1 point; drawing and losing give 0 points.
• At the end of the round, submissions with the minimum points leave the tournament. In case of a tie, the player with the least amount of points earned since the beginning of the tournament will leave.
• If more than one player is left, the next round shall begin.
• Points do NOT carry over to the next round.

Submission

You'll submit one player per answer. You can submit multiple files for a player, as long as they do NOT interfere with other submissions. To keep things flowing, please:

• Name your main header file as <Custom>Player.hpp,
• Name your other files as <Custom>Player*.*, e.g. MyLittlePlayer.txt if your class name is MyLittlePlayer, or EmoPlayerHates.cpp if your class name is EmoPlayer.
• If your name contains Shooter or similar words that fit the context of this tournament, you need not add Player at the end. If you feel strongly that your submission name works better without the suffix Player, you also don't need to add Player.
• Make sure that your code can be compiled and linked under Windows.

You can comment to ask for clarification or to spot loopholes. Hope you enjoy this Futuristic Gun Duel and wish you a Happy New Year!

Clarification

• You are allowed to have randomized behavior.
• Invalid actions (firing when loaded ammo isn't enough) are allowed.
• If a player makes an invalid input, their gun will explode immediately.
• You are allowed to study the answers.
• You are explicitly allowed to record opponent behavior within each tournament.
• Each round, you will play 100 duels against each opponent; the order of the 100 duels, however, is randomized-- you're not guaranteed to fight the same opponent 100 duels in a row.

Additional Resources

@flawr has translated the provided C++ source into Java as a reference if you want to submit C++ entries.

Interface for Non-C++ Submissions

Currently accepted: Python 3, Java.

Please follow one of the specifications below:

Interface specification 1: exit code

Your submission will run once per turn.

Expected Command Line Argument Format:
    <opponent-id> <turn> <status> <ammo> <ammo-opponent> <history> <history-opponent>

Expected Return Code: The ASCII value of a valid action character.
    '0' = 48, '1' = 49, '2' = 50, '-' = 45, '=' = 61

<opponent-id> is an integer in [0, N), where N is size of tournament.
<turn> is 0-based.
If duel is in progress, <status> is 3.
If duel is draw / won / lost, <status> is 0 / 1 / 2.
<history> and <history-opponent> are strings of actions, e.g. 002 0-=
If turn is 0, <history> and <history-opponent> are not provided.
You can ignore arguments you don't particularly need.

You can test your submission in PythonPlayer\ and JavaPlayer\ directories.

Interface specification 2: stdin/stdout

(Credit to H Walters)

Your submission will run once per tournament.

There's a fixed requirement for all entries on how to do I/O, since both stdin and stdout are connected to the tournament driver. Violating this could lead to a deadlock. All entries MUST follow this EXACT algorithm (in pseudo-code):

LOOP FOREVER
    READ LINE INTO L
    IF (LEFT(L,1) == 'I')
        INITIALIZE ROUND
        // i.e., set your/opponent ammo to 0, if tracking them
        // Note: The entire line at this point is a unique id per opponent;
        // optionally track this as well.
        CONTINUE LOOP
    ELSE IF (LEFT(L,1) == 'F')
        WRITELN F // where F is your move
    ELSE IF (LEFT(L,1) == 'P')
        PROCESS MID(L,2,1) // optionally perceive your opponent's action.
    END IF
CONTINUE LOOP
QUIT

Here, F is one of 0, 1, 2, -, or = for load / bullet / plasma / metal / thermal. PROCESS means to optionally respond to what your opponent did (including tracking your opponent's ammo if you're doing this). Note that the opponent's action is also one of '0', '1', '2', '-', or '=', and is in the second character.

Final Scoreboard

08:02 AM Tuesday, February 2, 2017 Coordinated Universal Time (UTC)
| Player             | Language   | Points |     1 |     2 |     3 |     4 |     5 |     6 |     7 |     8 |     9 |    10 |    11 |    12 |    13 |    14 |    15 |    16 |
|:------------------ |:---------- | ------:| -----:| -----:| -----:| -----:| -----:| -----:| -----:| -----:| -----:| -----:| -----:| -----:| -----:| -----:| -----:| -----:|
| MontePlayer        | C++        |  11413 |  1415 |  1326 |  1247 |  1106 |  1049 |   942 |   845 |   754 |   685 |   555 |   482 |   381 |   287 |   163 |   115 |    61 |
| CBetaPlayer        | C++        |   7014 |   855 |   755 |   706 |   683 |   611 |   593 |   513 |   470 |   414 |   371 |   309 |   251 |   192 |   143 |   109 |    39 |
| StudiousPlayer     | C++        |  10014 |  1324 |  1233 |  1125 |  1015 |   907 |   843 |   763 |   635 |   555 |   478 |   403 |   300 |   201 |   156 |    76 |
| FatedPlayer        | C++        |   6222 |   745 |   683 |   621 |   655 |   605 |   508 |   494 |   456 |   395 |   317 |   241 |   197 |   167 |   138 |
| HanSoloPlayer      | C++        |   5524 |   748 |   668 |   584 |   523 |   490 |   477 |   455 |   403 |   335 |   293 |   209 |   186 |   153 |
| SurvivorPlayer     | C++        |   5384 |   769 |   790 |   667 |   574 |   465 |   402 |   354 |   338 |   294 |   290 |   256 |   185 |
| SpecificPlayer     | C++        |   5316 |   845 |   752 |   669 |   559 |   488 |   427 |   387 |   386 |   340 |   263 |   200 |
| DeceptivePlayer    | C++        |   4187 |   559 |   445 |   464 |   474 |   462 |   442 |   438 |   369 |   301 |   233 |
| NotSoPatientPlayer | C++        |   5105 |   931 |   832 |   742 |   626 |   515 |   469 |   352 |   357 |   281 |
| BarricadePlayer    | C++        |   4171 |   661 |   677 |   614 |   567 |   527 |   415 |   378 |   332 |
| BotRobotPlayer     | C++        |   3381 |   607 |   510 |   523 |   499 |   496 |   425 |   321 |
| SadisticShooter    | C++        |   3826 |   905 |   780 |   686 |   590 |   475 |   390 |
| TurtlePlayer       | C++        |   3047 |   754 |   722 |   608 |   539 |   424 |
| CamtoPlayer        | C++        |   2308 |   725 |   641 |   537 |   405 |
| OpportunistPlayer  | C++        |   1173 |   426 |   420 |   327 |
| GunClubPlayer      | C++        |    888 |   500 |   388 |
| PlasmaPlayer       | C++        |    399 |   399 |

The tournament will last till February 1, 2017 unless otherwise noted.

Answer 1

The BlackHatPlayer

The BlackHat Player knows that bullets and shields are a thing of the past; the actual wars are won by those who can hack the opponent's programs.

So, he puts on a fixed metal shield and starts doing his thing.

The first time he is asked to fight, he tries to localize his enemy in memory. Given the structure of the fighting arena, it's almost sure that the compiler will end up putting his address (wrapped in an unique_ptr) and the one of the opponent just one next to the other.

So, the BlackHat walks carefully the stack, using some simple heuristics to make sure not to underflow it, until he finds a pointer to himself; then checks if the values in the adjacent positions are plausibly his opponent - similar address, similar address of the vtable, plausible typeid.

If it manages to find him, he sucks his brains out and replaces them with the ones of a hothead idiot. In practice, this is done by replacing the opponent's pointer to the vtable with the address of the Idiot vtable - a dumb player who always shoots.

If this all succeeds (and in my tests - gcc 6 on Linux 64 bit, MinGW 4.8 on wine 32 bit - this works quite reliably), the war is won. Whatever the opponent did at the first round is not important - at worst he shot us, and we had the metal shield on.

From now on, we have an idiot just shooting; we always have our shield on, so we are protected, and he'll blow up in 1 to 3 rounds (depending on what the original bot did in his first fight call).

---

Now: I'm almost sure that this should be disqualified immediately, but it's funny that I'm not explicitly violating any of the rules stated above:

What you must NOT do

• You must NOT use any direct method to recognize your opponent other than the given opponent identifier, which is completely randomized at the beginning of each tournament. You're only allowed to guess who a player is through their gameplay within a tournament.

BlackHat does not try to recognize the opponent - actually, it's completely irrelevant who the opponent is, given that his brain is replaced immediately.

• You must NOT override any methods in Player class that is not declared virtual.
• You must NOT declare or initialize anything in the global scope.

Everything happens locally to the fight virtual function.

---

// BlackHatPlayer.hpp

#ifndef __BLACKHAT_PLAYER_HPP__
#define __BLACKHAT_PLAYER_HPP__

#include "Player.hpp"
#include <stddef.h>
#include <typeinfo>
#include <algorithm>
#include <string.h>

class BlackHatPlayer final : public Player
{
public:
    using Player::Player;

    virtual Action fight()
    {
        // Always metal; if the other is an Idiot, he only shoots,
        // and if he isn't an Idiot yet (=first round) it's the only move that
        // is always safe
        if(tricked) return metal();
        // Mark that at the next iterations we don't have to do all this stuff
        tricked = true;

        typedef uintptr_t word;
        typedef uintptr_t *pword;
        typedef uint8_t *pbyte;

        // Size of one memory page; we use it to walk the stack carefully
        const size_t pageSize = 4096;
        // Maximum allowed difference between the vtables
        const ptrdiff_t maxVTblDelta = 65536;
        // Maximum allowed difference between this and the other player
        ptrdiff_t maxObjsDelta = 131072;

        // Our adversary
        Player *c = nullptr;

        // Gets the start address of the memory page for the given object
        auto getPage = [&](void *obj) {
            return pword(word(obj) & (~word(pageSize-1)));
        };
        // Gets the start address of the memory page *next* to the one of the given object
        auto getNextPage = [&](void *obj) {
            return pword(pbyte(getPage(obj)) + pageSize);
        };

        // Gets a pointer to the first element of the vtable
        auto getVTbl = [](void *obj) {
            return pword(pword(obj)[0]);
        };

        // Let's make some mess to make sure that:
        // - we have an actual variable on the stack;
        // - we call an external (non-inline) function that ensures everything
        //   is spilled on the stack
        // - the compiler actually generates the full vtables (in the current
        //   tournament this shouldn't be an issue, but in earlier sketches
        //   the compiler inlined everything and killed the vtables)
        volatile word i = 0;
        for(const char *sz = typeid(*(this+i)).name(); *sz; ++sz) i+=*sz;

        // Grab my vtable
        word *myVTbl = getVTbl(this);

        // Do the stack walk
        // Limit for the stack walk; use i as a reference
        word *stackEnd = getNextPage((pword)(&i));
        for(word *sp = pword(&i);       // start from the location of i
            sp!=stackEnd && c==nullptr;
            ++sp) {                     // assume that the stack grows downwards
            // If we find something that looks like a pointer to memory
            // in a page just further on the stack, take it as a clue that the
            // stack in facts does go on
            if(getPage(pword(*sp))==stackEnd) {
                stackEnd = getNextPage(pword(*sp));
            }
            // We are looking for our own address on the stack
            if(*sp!=(word)this) continue;

            auto checkCandidate = [&](void *candidate) -> Player* {
                // Don't even try with NULLs and the like
                if(getPage(candidate)==nullptr) return nullptr;
                // Don't trust objects too far away from us - it's probably something else
                if(abs(pbyte(candidate)-pbyte(this))>maxObjsDelta) return nullptr;
                // Grab the vtable, check if it actually looks like one (it should be
                // decently near to ours)
                pword vtbl = getVTbl(candidate);
                if(abs(vtbl-myVTbl)>maxVTblDelta) return nullptr;
                // Final check: try to see if its name looks like a "Player"
                Player *p = (Player *)candidate;
                if(strstr(typeid(*p).name(), "layer")==0) return nullptr;
                // Jackpot!
                return p;
            };

            // Look around us - a pointer to our opponent should be just near
            c = checkCandidate((void *)sp[-1]);
            if(c==nullptr) c=checkCandidate((void *)sp[1]);
        }

        if(c!=nullptr) {
            // We found it! Suck his brains out and put there the brains of a hothead idiot
            struct Idiot : Player {
                virtual Action fight() {
                    // Always fire, never reload; blow up in two turns
                    // (while we are always using the metal shield to protect ourselves)
                    return bullet();
                }
            };
            Idiot idiot;
            // replace the vptr
            (*(word *)(c)) = word(getVTbl(&idiot));
        }
        // Always metal shield to be protected from the Idiot
        return metal();
    }
private:
    bool tricked = false;
};

#endif // !__BLACKHAT_PLAYER_HPP__

Answer 2

Next, the most feared of all creatures, it's been to hell and back and fought with literally 900000 other bots, its...

The BotRobot

BotRobot was named, trained and built automatically by a very basic Genetic algorithm.

Two teams of 9 were set up against eachother, in each generation, each robot from team 1 is put up against each robot of team 2. The robots with more wins than losses, kept its memory, the other, reverted back to the last step, and had a chance to forget something, hopefully bad. The bots themselves are glorified lookup tables, where if they found something they hadn't seen before, they'd simply pick a random valid option and save it to memory. The C++ version does not do this, it should have learned. As stated before, winning bots keep this new found memory, as clearly it worked. Losing bots don't, and keep what they started with.

In the end, the bot fights were fairly close, rarely stalemating. The winner was picked out of a pool of the two teams post evolution, which was 100000 generations.

BotRobot, with its randomly generated and BEAUTIFUL name, was the lucky one.

Generator

bot.lua

Revision: Although the robot was fairly smart against himself and other similarly generated robots, he proved fairly useless in actual battles. So, I regenerated his brain against some of the already created bots.

The results, as can easily be seen, is a much more complex brain, with options up to the enemy player having 12 ammo.

I'm not sure what he was fighting against that got up to 12 ammo, but something did.

And of course, the finished product...

// BotRobot
// ONE HUNDRED THOUSAND GENERATIONS TO MAKE THE ULTIMATE LIFEFORM!

#ifndef __BOT_ROBOT_PLAYER_HPP__
#define __BOT_ROBOT_PLAYER_HPP__

#include "Player.hpp"

class BotRobotPlayer final : public Player
{
public:
    BotRobotPlayer(size_t opponent = -1) : Player(opponent) {}

public:
    virtual Action fight()
    {
        std::string action = "";
        action += std::to_string(getAmmo());
        action += ":";
        action += std::to_string(getAmmoOpponent());

        int toDo = 3;

        for (int i = 0; i < int(sizeof(options)/sizeof(*options)); i++) {
            if (options[i].compare(action)==0) {
                toDo = outputs[i];
                break;
            }
        }

        switch (toDo) {
            case 0:
                return load();
            case 1:
                return bullet();
            case 2:
                return plasma();
            case 3:
                return metal();
            default:
                return thermal();
        }
    }

private:
    std::string options[29] =
    {
        "0:9",
        "1:12",
        "1:10",
        "0:10",
        "1:11",
        "0:11",
        "0:6",
        "2:2",
        "0:2",
        "2:6",
        "3:6",
        "0:7",
        "1:3",
        "2:3",
        "0:3",
        "2:0",
        "1:0",
        "0:4",
        "1:4",
        "2:4",
        "0:0",
        "3:0",
        "1:1",
        "2:1",
        "2:9",
        "0:5",
        "0:8",
        "3:1",
        "0:1"
    };

    int outputs[29] =
    {
        0,
        1,
        1,
        4,
        1,
        0,
        0,
        4,
        4,
        0,
        0,
        3,
        0,
        1,
        3,
        0,
        1,
        4,
        0,
        1,
        0,
        1,
        0,
        3,
        4,
        3,
        0,
        1,
        0
    };
};

#endif // !__BOT_ROBOT_PLAYER_HPP__

I hate C++ now...

Answer 3

CBetaPlayer (cβ)

Approximate Nash Equilibrium.

This bot is just fancy math with a code wrapper.

We can reframe this as a game theory problem. Denote a win by +1 and a loss by -1. Now let B(x, y) be the value of the game where we have x ammo and our opponent has y ammo. Note that B(a, b) = -B(b, a) and so B(a, a) = 0. To find B values in terms of other B values, we can compute the value of the payoff matrix. For example, we have that B(1, 0) is given by the value of the following subgame:

       load      metal
load    B(0, 1)   B(2, 0)
bullet  +1        B(0, 0)

(I've removed the "bad" options, aka the ones which are strictly dominated by the existing solutions. For example, we would not try to shoot plasma since we only have 1 ammo. Likewise our opponent would never use a thermal deflector, since we will never shoot plasma.)

Game theory lets us know how to find the value of this payoff matrix, assuming certain technical conditions. We get that the value of the above matrix is:

                B(2, 0)
B(1, 0) = ---------------------
          1 + B(2, 0) - B(2, 1)

Proceeding for all possible games and noting that B(x, y) -> 1 as x -> infinity with y fixed, we can find all the B values, which in turn lets us compute the perfect moves!

Of course, theory rarely lines up with reality. Solving the equation for even small values of x and y quickly becomes too complicated. In order to deal with this, I introduced what I call the cβ-approximation. There are 7 parameters to this approximation: c0, β0, c1, β1, c, β and k. I assumed that the B values took the following form (most specific forms first):

B(1, 0) = k
B(x, 0) = 1 - c0 β0^x
B(x, 1) = 1 - c1 β1^x
B(x, y) = 1 - c β^(x - y)   (if x > y)

Some rough reasoning on why I chose these parameters. First I knew that I definitely wanted to deal with having 0, 1 and 2 or more ammo separately, since each opens different options. Also I thought a geometric survival function would be the most appropriate, because the defensive player is essentially guessing what move to make. I figured that having 2 or more ammo was basically the same, so I focused on the difference instead. I also wanted to treat B(1, 0) as a super special case because I thought it would show up a lot. Using these approximate forms simplified the calculations of the B values greatly.

I approximately solved the resulting equations to get each B value, which I then put back into the matrix in order to get the payoff matrices. Then using a linear programing solver, I found the optimal probabilities to make each move and shoved them into the program.

The program is a glorified lookup table. If both players have between 0 and 4 ammo, it uses the probability matrix to randomly determine which move it should make. Otherwise, it tries to extrapolate based on its table.

It has trouble against stupid deterministic bots, but does pretty well against rational bots. Because of all the approximation, this will occasionally lose to StudiousPlayer when it really shouldn't.

Of course, if I was to do this again I would probably try to add more independent parameters or perhaps a better ansatz form and come up with a more exact solution. Also I (purposely) ignored the turn-limit, because it made things harder. A quick modification could be made to always shoot plasma if we have enough ammo and there aren't enough turns left.

// CBetaPlayer (cβ)
// PPCG: George V. Williams

#ifndef __CBETA_PLAYER_HPP__
#define __CBETA_PLAYER_HPP__

#include "Player.hpp"
#include <iostream>

class CBetaPlayer final : public Player
{
public:
    CBetaPlayer(size_t opponent = -1) : Player(opponent)
    {
    }

public:
    virtual Action fight()
    {
        int my_ammo = getAmmo(), opp_ammo = getAmmoOpponent();

        while (my_ammo >= MAX_AMMO || opp_ammo >= MAX_AMMO) {
            my_ammo--;
            opp_ammo--;
        }

        if (my_ammo < 0) my_ammo = 0;
        if (opp_ammo < 0) opp_ammo = 0;

        double cdf = GetRandomDouble();
        int move = -1;
        while (cdf > 0 && move < MAX_MOVES - 1)
            cdf -= probs[my_ammo][opp_ammo][++move];

        switch (move) {
            case 0: return load();
            case 1: return bullet();
            case 2: return plasma();
            case 3: return metal();
            case 4: return thermal();
            default: return fight();
        }
    }

    static double GetRandomDouble() {
        static auto seed = std::chrono::system_clock::now().time_since_epoch().count();
        static std::default_random_engine generator((unsigned)seed);
        std::uniform_real_distribution<double> distribution(0.0, 1.0);
        return distribution(generator);
    }

private:
    static const int MAX_AMMO = 5;
    static const int MAX_MOVES = 5;

    double probs[MAX_AMMO][MAX_AMMO][5] =
        {
            {{1, 0, 0, 0, 0}, {0.58359, 0, 0, 0.41641, 0}, {0.28835, 0, 0, 0.50247, 0.20918}, {0.17984, 0, 0, 0.54611, 0.27405}, {0.12707, 0, 0, 0.56275, 0.31018}},
            {{0.7377, 0.2623, 0, 0, 0}, {0.28907, 0.21569, 0, 0.49524, 0}, {0.0461, 0.06632, 0, 0.53336, 0.35422}, {0.06464, 0.05069, 0, 0.43704, 0.44763}, {0.02215, 0.038, 0, 0.33631, 0.60354}},
            {{0.47406, 0.37135, 0.1546, 0, 0}, {0.1862, 0.24577, 0.15519, 0.41284, 0}, {0, 0.28343, 0.35828, 0, 0.35828}, {0, 0.20234, 0.31224, 0, 0.48542}, {0, 0.12953, 0.26546, 0, 0.605}},
            {{0.33075, 0.44563, 0.22362, 0, 0}, {0.17867, 0.20071, 0.20071, 0.41991, 0}, {0, 0.30849, 0.43234, 0, 0.25916}, {0, 0.21836, 0.39082, 0, 0.39082}, {0, 0.14328, 0.33659, 0, 0.52013}},
            {{0.24032, 0.48974, 0.26994, 0, 0}, {0.14807, 0.15668, 0.27756, 0.41769, 0}, {0, 0.26804, 0.53575, 0, 0.19621}, {0, 0.22106, 0.48124, 0, 0.2977}, {0, 0.15411, 0.42294, 0, 0.42294}}
        };


};

#endif // !__CBETA_PLAYER_HPP__

Answer 4

MontePlayer

This player uses the Decoupled UCT Monte Carlo Tree Search algorithm to decide what choices it should make. It tracks what the enemy does to predict its actions. It simulates the enemy as itself if it lacks data.

This bot does really well against every other bot except cβ. In a 10000 duel match against cβ, Monte won 5246 duels. With a little bit of maths, that means that Monte will win a duel against cβ 51.17% to 53.74% of the time (99% confidence).

#ifndef __Monte_PLAYER_HPP__
#define __Monte_PLAYER_HPP__

#include "Player.hpp"
#include <cstdlib>
#include <ctime>
#include <memory>
#include <iostream>


class MontePlayer final : public Player
{
    static const int MAX_TURNS = 100;
    static const int TOTAL_ACTIONS = 5;

    //Increase this if number of players goes above 20.
    static const int MAX_PLAYERS = 20;

    //The number of simulated games we run every time our program is called.
    static const int MONTE_ROUNDS = 1000;


    /**
    * Represents the current state of the game.
    */
    struct Game
    {
        int turn;
        int ammo;
        int opponentAmmo;
        bool alive;
        bool opponentAlive;

        Game(int turn, int ammo, int opponentAmmo, bool alive, bool opponentAlive)
            : turn(turn), ammo(ammo), opponentAmmo(opponentAmmo), alive(alive), opponentAlive(opponentAlive) {}
        Game() : turn(0), ammo(0), opponentAmmo(0), alive(false), opponentAlive(false) {}
    };

    struct Stat
    {
        int wins;
        int attempts;

        Stat() : wins(0), attempts(0) {}
    };

    /**
    * A Monte tree data structure.
    */
    struct MonteTree
    {
        //The state of the game.
        Game game;

        //myStats[i] returns the statistic for doing the i action in this state.
        Stat myStats[TOTAL_ACTIONS];
        //opponentStats[i] returns the statistic for the opponent doing the i action in this state.
        Stat opponentStats[TOTAL_ACTIONS];
        //Total number of times we've created statistics from this tree.
        int totalPlays = 0;
        //The action that led to this tree.
        int myAction;
        //The opponent action that led to this tree.
        int opponentAction;

        //The tree preceding this one.
        MonteTree *parent = NULL;

        //subtrees[i][j] is the tree that would follow if I did action i and the
        //opponent did action j.
        MonteTree *subtrees[TOTAL_ACTIONS][TOTAL_ACTIONS] = { { NULL } };

        MonteTree(int turn, int ammo, int opponentAmmo) :
            game(turn, ammo, opponentAmmo, true, true) {}


        MonteTree(Game game, MonteTree *parent, int myAction, int opponentAction) :
            game(game), parent(parent), myAction(myAction), opponentAction(opponentAction)
        {
            //Make sure the parent tree keeps track of this tree.
            parent->subtrees[myAction][opponentAction] = this;
        }

        //The destructor so we can avoid slow ptr types and memory leaks.
        ~MonteTree()
        {
            //Delete all subtrees.
            for (int i = 0; i < TOTAL_ACTIONS; i++)
            {
                for (int j = 0; j < TOTAL_ACTIONS; j++)
                {
                    auto branch = subtrees[i][j];

                    if (branch)
                    {
                        branch->parent = NULL;
                        delete branch;
                    }
                }
            }
        }
    };

    //The previous state.
    Game prevGame;
    //The id of the opponent.
    int opponent;
    //opponentHistory[a][b][c][d] returns the number of times
    //that opponent a did action d when I had b ammo and he had c ammo.
    static int opponentHistory[MAX_PLAYERS][MAX_TURNS][MAX_TURNS][TOTAL_ACTIONS];

public:
    MontePlayer(size_t opponent = -1) : Player(opponent)
    {
        srand(time(NULL));
        this->opponent = opponent;
    }

public:

    virtual Action fight()
    {
        //Create the root tree. Will be auto-destroyed after this function ends.
        MonteTree current(getTurn(), getAmmo(), getAmmoOpponent());

        //Set the previous game to this one.
        prevGame = current.game;

        //Get these variables so we can log later if nessecarry.
        int turn = getTurn(),
            ammo = getAmmo(),
            opponentAmmo = getAmmoOpponent();

        for (int i = 0; i < MONTE_ROUNDS; i++)
        {
            //Go down the tree until we find a leaf we haven't visites yet.
            MonteTree *leaf = selection(&current);

            //Randomly simulate the game at the leaf and get the result.
            int score = simulate(leaf->game);

            //Propagate the scores back up the root.
            update(leaf, score);
        }

        //Get the best move.
        int move = bestMove(current);

        //Move string for debugging purposes.
        const char* m;

        //We have to do this so our bots state is updated.
        switch (move)
        {
        case Action::LOAD:
            load();
            m = "load";
            break;
        case Action::BULLET:
            bullet();
            m = "bullet";
            break;
        case Action::PLASMA:
            plasma();
            m = "plasma";
            break;
        case Action::METAL:
            metal();
            m = "metal";
            break;
        case Action::THERMAL:
            thermal();
            m = "thermal";
            break;
        default: //???
            std::cout << move << " ???????\n";
            throw move;
        }

        return (Action)move;
    }

    /**
    * Record what the enemy does so we can predict him.
    */
    virtual void perceive(Action action)
    {
        Player::perceive(action);
        opponentHistory[opponent][prevGame.ammo][prevGame.opponentAmmo][action]++;
    }
private:

    /**
    * Trickle down root until we have to create a new leaf MonteTree or we hit the end of a game.
    */
    MonteTree * selection(MonteTree *root)
    {
        while (!atEnd(root->game))
        {
            //First pick the move that my bot will do.

            //The action my bot will do.
            int myAction;
            //The number of actions with the same bestScore.
            int same = 0;
            //The bestScore
            double bestScore = -1;

            for (int i = 0; i < TOTAL_ACTIONS; i++)
            {
                //Ignore invalid or idiot moves.
                if (!isValidMove(root->game, i, true))
                {
                    continue;
                }

                //Get the score for doing move i. Uses
                double score = computeScore(*root, i, true);

                //Randomly select one score if multiple actions have the same score.
                //Why this works is boring to explain.
                if (score == bestScore)
                {
                    same++;
                    if (Random(same) == 0)
                    {
                        myAction = i;
                    }
                }
                //Yay! We found a better action.
                else if (score > bestScore)
                {
                    same = 1;
                    myAction = i;
                    bestScore = score;
                }
            }

            //The action the enemy will do.
            int enemyAction;

            //The number of times the enemy has been in this same situation.
            int totalEnemyEncounters = 0;
            for (int i = 0; i < TOTAL_ACTIONS; i++)
            {
                totalEnemyEncounters += opponentHistory[opponent][root->game.ammo][root->game.opponentAmmo][i];
            }

            //Assume the enemy will choose an action it has chosen before if we've
            //seen it in this situation before. Otherwise we assume that the enemy is ourselves.
            if (totalEnemyEncounters > 0)
            {
                //Randomly select an action that the enemy has done with
                //weighted by the number of times that action has been done.
                int selection = Random(totalEnemyEncounters);
                for (int i = 0; i < TOTAL_ACTIONS; i++)
                {
                    selection -= opponentHistory[opponent][root->game.ammo][root->game.opponentAmmo][i];
                    if (selection < 0)
                    {
                        enemyAction = i;
                        break;
                    }
                }
            }
            else
            {
                //Use the same algorithm to pick the enemies move we use for ourselves.
                same = 0;
                bestScore = -1;
                for (int i = 0; i < TOTAL_ACTIONS; i++)
                {
                    if (!isValidMove(root->game, i, false))
                    {
                        continue;
                    }

                    double score = computeScore(*root, i, false);
                    if (score == bestScore)
                    {
                        same++;
                        if (Random(same) == 0)
                        {
                            enemyAction = i;
                        }
                    }
                    else if (score > bestScore)
                    {
                        same = 1;
                        enemyAction = i;
                        bestScore = score;
                    }
                }
            }

            //If this combination of actions hasn't been explored yet, create a new subtree to explore.
            if (!(*root).subtrees[myAction][enemyAction])
            {
                return expand(root, myAction, enemyAction);
            }

            //Do these actions and explore the next subtree.
            root = (*root).subtrees[myAction][enemyAction];
        }
        return root;
    }

    /**
    * Creates a new leaf under root for the actions.
    */
    MonteTree * expand(MonteTree *root, int myAction, int enemyAction)
    {
        return new MonteTree(
            doTurn(root->game, myAction, enemyAction),
            root,
            myAction,
            enemyAction);
    }

    /**
    * Computes the score of the given move in the given position.
    * Uses the UCB1 algorithm and returns infinity for moves not tried yet.
    */
    double computeScore(const MonteTree &root, int move, bool me)
    {
        const Stat &stat = me ? root.myStats[move] : root.opponentStats[move];
        return stat.attempts == 0 ?
            HUGE_VAL :
            double(stat.wins) / stat.attempts + sqrt(2 * log(root.totalPlays) / stat.attempts);
    }

    /**
    * Randomly simulates the given game.
    * Has me do random moves that are not stupid.
    * Has opponent do what it has done in similar positions or random moves if not
    * observed in those positions yet.
    *
    * Returns 1 for win. 0 for loss. -1 for draw.
    */
    int simulate(Game game)
    {
        while (!atEnd(game))
        {
            game = doRandomTurn(game);
        }

        if (game.alive > game.opponentAlive)
        {
            return 1;
        }
        else if (game.opponentAlive > game.alive)
        {
            return 0;
        }
        else //Draw
        {
            return -1;
        }
    }

    /**
    * Returns whether the game is over or not.
    */
    bool atEnd(Game game)
    {
        return !game.alive || !game.opponentAlive || game.turn > MAX_TURNS;
    }

    /**
    * Simulates the given actions on the game.
    */
    Game doTurn(Game game, int myAction, int enemyAction)
    {
        game.turn++;

        switch (myAction)
        {
        case Action::LOAD:
            game.ammo++;
            break;
        case Action::BULLET:
            if (game.ammo < 1)
            {
                game.alive = false;
                break;
            }
            game.ammo--;
            if (enemyAction == Action::LOAD || enemyAction == Action::THERMAL)
            {
                game.opponentAlive = false;
            }
            break;
        case Action::PLASMA:
            if (game.ammo < 2)
            {
                game.alive = false;
                break;
            }
            game.ammo -= 2;
            if (enemyAction != Action::PLASMA && enemyAction != Action::THERMAL)
            {
                game.opponentAlive = false;
            }
            break;
        }

        switch (enemyAction)
        {
        case Action::LOAD:
            game.opponentAmmo++;
            break;
        case Action::BULLET:
            if (game.opponentAmmo < 1)
            {
                game.opponentAlive = false;
                break;
            }
            game.opponentAmmo--;
            if (myAction == Action::LOAD || myAction == Action::THERMAL)
            {
                game.alive = false;
            }
            break;
        case Action::PLASMA:
            if (game.opponentAmmo < 2)
            {
                game.opponentAlive = false;
            }
            game.opponentAmmo -= 2;
            if (myAction != Action::PLASMA && myAction != Action::THERMAL)
            {
                game.alive = false;
            }
            break;
        }

        return game;
    }

    /**
    * Chooses a random move for me and my opponent and does it.
    */
    Game doRandomTurn(Game &game)
    {
        //Select my random move.
        int myAction;
        int validMoves = 0;

        for (int i = 0; i < TOTAL_ACTIONS; i++)
        {
            //Don't do idiotic moves.
            //Select one at random.
            if (isValidMove(game, i, true))
            {
                validMoves++;
                if (Random(validMoves) == 0)
                {
                    myAction = i;
                }
            }
        }

        //Choose random opponent action.
        int opponentAction;

        //Whether the enemy has encountered this situation before
        bool enemyEncountered = false;

        validMoves = 0;

        //Weird algorithm that works and I don't want to explain.
        //What it does:
        //If the enemy has encountered this position before,
        //then it chooses a random action weighted by how often it did that action.
        //If they haven't, makes the enemy choose a random not idiot move.
        for (int i = 0; i < TOTAL_ACTIONS; i++)
        {
            int weight = opponentHistory[opponent][game.ammo][game.opponentAmmo][i];
            if (weight > 0)
            {
                if (!enemyEncountered)
                {
                    enemyEncountered = true;
                    validMoves = 0;
                }
                validMoves += weight;
                if (Random(validMoves) < weight)
                {
                    opponentAction = i;
                }
            }
            else if (!enemyEncountered && isValidMove(game, i, false))
            {
                validMoves++;
                if (Random(validMoves) == 0)
                {
                    opponentAction = i;
                }
            }
        }

        return doTurn(game, myAction, opponentAction);
    }

    /**
    * Returns whether the given move is valid/not idiotic for the game.
    */
    bool isValidMove(Game game, int move, bool me)
    {
        switch (move)
        {
        case Action::LOAD:
            return true;
        case Action::BULLET:
            return me ? game.ammo > 0 : game.opponentAmmo > 0;
        case Action::PLASMA:
            return me ? game.ammo > 1 : game.opponentAmmo > 1;
        case Action::METAL:
            return me ? game.opponentAmmo > 0 : game.ammo > 0;
        case Action::THERMAL:
            return me ? game.opponentAmmo > 1 : game.ammo > 1;
        default:
            return false;
        }
    }

    /**
    * Propagates the score up the MonteTree from the leaf.
    */
    void update(MonteTree *leaf, int score)
    {
        while (true)
        {
            MonteTree *parent = leaf->parent;
            if (parent)
            {
                //-1 = draw, 1 = win for me, 0 = win for opponent
                if (score != -1)
                {
                    parent->myStats[leaf->myAction].wins += score;
                    parent->opponentStats[leaf->opponentAction].wins += 1 - score;
                }
                parent->myStats[leaf->myAction].attempts++;
                parent->opponentStats[leaf->opponentAction].attempts++;
                parent->totalPlays++;
                leaf = parent;
            }
            else
            {
                break;
            }
        }
    }

    /**
    * There are three different strategies in here.
    * The first is not random, the second more, the third most.
    */
    int bestMove(const MonteTree &root)
    {
        //Select the move with the highest win rate.
        int best;
        double bestScore = -1;
        for (int i = 0; i < TOTAL_ACTIONS; i++)
        {
            if (root.myStats[i].attempts == 0)
            {
                continue;
            }

            double score = double(root.myStats[i].wins) / root.myStats[i].attempts;
            if (score > bestScore)
            {
                bestScore = score;
                best = i;
            }
        }

        return best;

        ////Select a move weighted by the number of times it has won the game.
        //int totalScore = 0;
        //for (int i = 0; i < TOTAL_ACTIONS; i++)
        //{
        //  totalScore += root.myStats[i].wins;
        //}
        //int selection = Random(totalScore);
        //for (int i = 0; i < TOTAL_ACTIONS; i++)
        //{
        //  selection -= root.myStats[i].wins;
        //  if (selection < 0)
        //  {
        //      return i;
        //  }
        //}

        ////Select a random move weighted by win ratio.
        //double totalScore = 0;
        //for (int i = 0; i < TOTAL_ACTIONS; i++)
        //{
        //  if (root.myStats[i].attempts == 0)
        //  {
        //      continue;
        //  }
        //  totalScore += double(root.myStats[i].wins) / root.myStats[i].attempts;
        //}
        //double selection = Random(totalScore);
        //for (int i = 0; i < TOTAL_ACTIONS; i++)
        //{
        //  if (root.myStats[i].attempts == 0)
        //  {
        //      continue;
        //  }
        //  selection -= double(root.myStats[i].wins) / root.myStats[i].attempts;
        //  if (selection < 0)
        //  {
        //      return i;
        //  }
        //}
    }

    //My own random functions.
    int Random(int max)
    {
        return GetRandomInteger(max - 1);
    }
    double Random(double max)
    {
        static auto seed = std::chrono::system_clock::now().time_since_epoch().count();
        static std::default_random_engine generator((unsigned)seed);
        std::uniform_real_distribution<double> distribution(0.0, max);
        return distribution(generator);
    }
};
//We have to initialize this here for some reason.
int MontePlayer::opponentHistory[MAX_PLAYERS][MAX_TURNS][MAX_TURNS][TOTAL_ACTIONS]{ { { { 0 } } } };

#endif // !__Monte_PLAYER_HPP__

Answer 5

I'm lacking the comment everywhere right, so I can't ask my questions yet. So this is a very basic player to win against the first bot.

[Edit] Thanks, now the previous status isn't true anymore but I think it's better to keep it so we can understand the context of this bot.

The Opportunist

The opportunist frequents the same gun club as the GunClubPlayers, however, he betted to a newcomer that he could beat every GunClubPlayers. So he exploit the habit he has long noticed and force himself not to shoot but wait just a little to win.

#ifndef __OPPORTUNIST_PLAYER_HPP__
#define __OPPORTUNIST_PLAYER_HPP__

#include <string>
#include <vector>

class OpportunistPlayer final: public Player
{
public:
    OpportunistPlayer(size_t opponent = -1) : Player(opponent) {}

public:
    virtual Action fight()
    {
        switch (getTurn() % 3)
        {
        case 0:
            return load();
            break;
        case 1:
            return metal();
            break;
        case 2:
            return bullet();
            break;
        }
        return plasma();
    }
};
#endif // !__OPPORTUNIST_PLAYER_HPP__

Answer 6

The BarricadePlayer

The Barricade Player loads a bullet first round, then keeps an appropiate shield (still a bit random). He also loads another shot every 5th round. Every round, there is a 15% chance to ignore the algoritm (except for reload first turn) and shoot a bullet. When enemy has no ammo, it loads. If somehow everything goes wrong, oh boy, he just shoots.

Newest changes:

Improved random numbers (thanks Frenzy Li).

// BarricadePlayer by devRicher
// PPCG: http://codegolf.stackexchange.com/a/104909/11933

// BarricadePlayer.hpp
// A very tactical player.

#ifndef __BARRICADE_PLAYER_HPP__
#define __BARRICADE_PLAYER_HPP__

#include "Player.hpp"
#include <cstdlib>
#include <ctime>

class BarricadePlayer final : public Player
{
public:
    BarricadePlayer(size_t opponent = -1) : Player(opponent) {}

public:
    virtual Action fight()
    {
        srand(time(NULL));
        if (getTurn() == 0) { return load(); }
        int r = GetRandomInteger(99) + 1; //Get a random
        if ((r <= 15) && (getAmmo() > 0)) { return bullet(); } //Override any action, and just shoot
        else
        {
            if (getTurn() % 5 == 0) //Every first and fifth turn
                return load();
            if (getAmmoOpponent() == 1) return metal();
            if (getAmmoOpponent() > 1) { return r <= 50 ? metal() : thermal(); }
            if (getAmmoOpponent() == 0) return load();

        }
        return bullet();
    }
};

#endif // !__BARRICADE_PLAYER_HPP__

Answer 7

The StudiousPlayer

The Studious Player studies its prey, modeling each opponent it encounters. This player begins with a basic strategy, randomly driven in places, and progresses to simple adaptive strategies based on frequentist measures of opponent response. It uses a simple model of opponents based on how they react to ammo combinations.

#ifndef __STUDIOUS_PLAYER_H__
#define __STUDIOUS_PLAYER_H__

#include "Player.hpp"
#include <unordered_map>

class StudiousPlayer final : public Player
{
public:
   using Player::GetRandomInteger;
   // Represents an opponent's action for a specific state.
   struct OpponentAction {
      OpponentAction(){}
      unsigned l=0;
      unsigned b=0;
      unsigned p=0;
      unsigned m=0;
      unsigned t=0;
   };
   // StudiousPlayer models every opponent that it plays,
   // and factors said model into its decisions.
   //
   // There are 16 states, corresponding to
   // 4 inner states (0,1,2,3) and 4 outer states
   // (0,1,2,3). The inner states represent our
   // (SP's) ammo; the outer represents the
   // Opponent's ammo.  For the inner or outer
   // states, 0-2 represent the exact ammo; and
   // 3 represents "3 or more".
   //
   // State n is (4*outer)+inner.
   //
   // State 0 itself is ignored, since we don't care
   // what action the opponent takes (we always load);
   // thus, it's not represented here.
   //
   // os stores states 1 through 15 (index 0 through 14).
   struct Opponent {
      std::vector<OpponentAction> os;
      Opponent() : os(15) {}
   };
   StudiousPlayer(size_t opponent)
      : Player(opponent)
      , strat(storedLs()[opponent])
      , ammoOpponent()
   {
   }
   Player::Action fight() {
      // Compute the current "ammo state".
      // For convenience here (aka, readability in switch),
      // this is a two digit octal number.  The lso is the
      // inner state, and the mso the outer state.
      unsigned ss,os;
      switch (ammoOpponent) {
      default: os=030; break;
      case 2 : os=020; break;
      case 1 : os=010; break;
      case 0 : os=000; break;
      }
      switch (getAmmo()) {
      default: ss=003; break;
      case 2 : ss=002; break;
      case 1 : ss=001; break;
      case 0 : ss=000; break;
      }
      // Store the ammo state.  This has a side effect
      // of causing actn() to return an OpponentAction
      // struct, with the opponent's history during this
      // state.
      osa = os+ss;
      // Get the opponent action pointer
      const OpponentAction* a=actn(osa);
      // If there's no such action structure, assume
      // we're just supposed to load.
      if (!a) return load();
      // Apply ammo-state based strategies:
      switch (osa) {
      case 001:
         // If opponent's likely to load, shoot; else load
         if (a->l > a->m) return bullet();
         return load();
      case 002:
      case 003:
         // Shoot in the way most likely to kill (or randomly)
         if (a->t > a->m+a->l) return bullet();
         if (a->m > a->t+a->l) return plasma();
         if (GetRandomInteger(1)) return bullet();
         return plasma();
      case 010:
         // If opponent tends to load, load; else defend
         if (a->l > a->b) return load();
         return metal();
      case 011:
         // Shoot if opponent tends to load
         if (a->l > a->b+a->m) return bullet();
         // Defend if opponent tends to shoot
         if (a->b > a->l+a->m) return metal();
         // Load if opponent tends to defend
         if (a->m > a->b+a->l) return load();
         // Otherwise randomly respond
         if (!GetRandomInteger(2)) return metal();
         if (!GetRandomInteger(1)) return load(); 
         return bullet();                         
      case 012:
      case 013:
         // If opponent most often shoots, defend
         if (a->b > a->l+a->m+a->t) return metal();
         // If opponent most often thermals, use bullet
         if (a->t > a->m) return bullet();
         // If opponent most often metals, use plasma
         if (a->m > a->t) return plasma();
         // Otherwise use a random weapon
         return (GetRandomInteger(1))?bullet():plasma();
      case 020:
         // If opponent most often loads or defends, load
         if (a->l+a->m+a->t > a->b+a->p) return load();
         // If opponent most often shoots bullets, raise metal
         if (a->b > a->p) return metal();
         // If opponent most often shoots plasma, raise thermal
         if (a->p > a->b) return thermal();
         // Otherwise raise random defense
         return (GetRandomInteger(1))?metal():thermal();
      case 021:
      case 031:
         // If opponent loads more often than not,
         if (a->l > a->m+a->b+a->p) {
            // Tend to shoot (67%), but possibly load (33%)
            return (GetRandomInteger(2))?bullet():load();
         }
         // If opponent metals more often than loads or shoots, load
         if (a->m > a->l+a->b+a->p) return load();
         // If opponent thermals (shrug) more often than loads or shoots, load
         if (a->t > a->l+a->b+a->p) return load();
         // If opponent tends to shoot bullets, raise metal
         if (a->b > a->p) return metal();
         // If opponent tends to shoot plasma, raise thermal
         if (a->p > a->b) return thermal();
         // Raise random shield
         return (GetRandomInteger(2))?metal():thermal();
      case 022:
         // If opponent loads or thermals more often than not, shoot bullet
         if (a->l+a->t > a->b+a->p+a->m) return bullet();
         // If opponent loads or metals more often than not, shoot plasma
         if (a->l+a->m > a->b+a->p+a->t) return plasma();
         // If opponent shoots more than loads or defends, defend
         if (a->b+a->p > a->l+a->m+a->t) {
            if (a->b > a->p) return metal();
            if (a->p > a->b) return thermal();
            return (GetRandomInteger(1))?metal():thermal();
         }
         // If opponent defends more than opponent shoots, load
         if (a->m+a->t > a->b+a->p) return load();
         // Use random substrategy;
         // load(33%)
         if (GetRandomInteger(2)) return load();
         // defend(33%)
         if (GetRandomInteger(1)) {
            if (a->b > a->p) return metal();
            if (a->b > a->b) return thermal();
            return (GetRandomInteger(1))?metal():thermal();
         }
         // Shoot in a way that most often kills (or randomly)
         if (a->m > a->t) return plasma();
         if (a->t > a->m) return bullet();
         return (GetRandomInteger(1))?bullet():plasma();
      case 023:
         // If opponent loads or raises thermal more often than not, shoot bullets
         if (a->l+a->t > a->b+a->p+a->m) return bullet();
         // If opponent loads or raises metal more often than not, shoot plasma
         if (a->l+a->m > a->b+a->p+a->t) return plasma();
         // If opponent shoots more than loads or defends, defend
         if (a->b+a->p > a->l+a->m+a->t) {
            if (a->b > a->p) return metal();
            if (a->p > a->b) return thermal();
            return (GetRandomInteger(1))?metal():thermal();
         }
         // If opponent defends more than shoots, shoot
         if (a->m+a->t > a->b+a->p) {
            if (a->m > a->t) return plasma();
            if (a->t > a->m) return bullet();
            return GetRandomInteger(1)?bullet():plasma();
         }
         // 50% defend
         if (GetRandomInteger(1)) {
            if (a->b > a->p) return metal();
            return thermal();
         }
         // 50% shoot
         if (a->m > a->t) return plasma();
         if (a->t > a->m) return bullet();
         return (GetRandomInteger(1))?bullet():plasma();
      case 030:
         // If opponent loads or shields more often than not, load
         if (a->l+a->m+a->t > a->b+a->p) return load();
         // If opponent tends to shoot, defend
         if (a->b+a->p >= a->l+a->m+a->t) {
            if (a->b > a->p) return metal();
            if (a->p > a->b) return thermal();
            return (GetRandomInteger(1))?metal():thermal();
         }
         // Otherwise, randomly shield (50%) or load
         if (GetRandomInteger(1)) {
            return (GetRandomInteger(1))?metal():thermal();
         }
         return load();
      case 032:
         // If opponent loads or thermals more often than not, shoot bullets
         if (a->l+a->t > a->b+a->p+a->m) return bullet();
         // If opponent loads or metals more often than not, shoot plasma
         if (a->l+a->m > a->b+a->p+a->t) return plasma();
         // If opponent shoots more often than loads or shields, defend
         if (a->b+a->p > a->l+a->m+a->t) {
            if (a->b > a->p) return metal();
            if (a->p > a->b) return thermal();
            return (GetRandomInteger(1))?metal():thermal();
         }
         // If opponent shields more often than shoots, load
         if (a->m+a->t > a->b+a->p) return load();
         // Otherwise use random strategy
         if (GetRandomInteger(2)) return load();
         if (GetRandomInteger(1)) {
            if (a->b > a->p) return metal();
            return thermal();
         }
         if (a->m > a->t) return plasma();
         if (a->t > a->m) return bullet();
         return (GetRandomInteger(1))?bullet():plasma();
      case 033:
         {
            // At full 3 on 3, apply random strategy
            // weighted by opponent's histogram of this state...
            // (the extra 1 weights towards plasma)
            unsigned sr=
               GetRandomInteger
               (a->l+a->t+a->p+a->b+a->m+1);
            // Shoot bullets proportional to how much
            // opponent loads or defends using thermal
            if (sr < a->l+a->t) return bullet();
            sr-=(a->l+a->t);
            // Defend with thermal proportional to how
            // much opponent attacks with plasma (tending to
            // waste his ammo)
            if (sr < a->p) return thermal();
            // Shoot plasma proportional to how
            // much opponent shoots bullets or raises metal
            return plasma();
         }
      }
      // Should never hit this; but rather than ruin everyone's fun,
      // if we do, we just load
      return load();
   }
   // Complete override; we use our opponent's model, not history.
   void perceive(Player::Action action) {
      // We want the ammo but not the history; since
      // the framework (Player::perceive) is "all or nothing", 
      // StudiousPlayer just tracks the ammo itself
      switch (action) {
      default: break;
      case Player::LOAD:   ++ammoOpponent; break;
      case Player::BULLET: --ammoOpponent; break;
      case Player::PLASMA: ammoOpponent-=2; break;
      }
      // Now we get the opponent's action based
      // on the last (incoming) ammo state
      OpponentAction* a = actn(osa);
      // ...if it's null just bail
      if (!a) return;
      // Otherwise, count the action
      switch (action) {
      case Player::LOAD    : ++a->l; break;
      case Player::BULLET  : ++a->b; break;
      case Player::PLASMA  : ++a->p; break;
      case Player::METAL   : ++a->m; break;
      case Player::THERMAL : ++a->t; break;
      }
   }
private:
   Opponent& strat;
   OpponentAction* actn(unsigned octalOsa) {
      unsigned ndx = (octalOsa%4)+4*(octalOsa/8);
      if (ndx==0) return 0;
      --ndx;
      if (ndx<15) return &strat.os[ndx];
      return 0;
   }
   unsigned osa;
   unsigned ammoOpponent;
   // Welcome, non-C++ persons, to the "Meyers style singleton".
   // "theMap" is initialized (constructed; initially empty)
   // the first time the declaration is executed.
   static std::unordered_map<size_t, Opponent>& storedLs() {
      static std::unordered_map<size_t, Opponent> theMap;
      return theMap;
   }
};

#endif

Note that this tracks information about opponents according to the rules of the challenge; see the "Meyers style singleton" scoped "storedLs()" method at the bottom. (Some people were wondering how to do this; now you know!)

Answer 8

The GunClubPlayer

Cut out from the original question. This serves as an example of a minimalistic implementation of a derived player. This player will participate in the tournament.

The GunClubPlayers like to go to the gun club. During each duel, they would first load ammo, then fire a bullet, and repeat this process until the end of the world duel. They doen't actually care whether they win or not, and focus exclusively on having an enjoyable experience themselves.

// GunClubPlayer.hpp
// A gun club enthusiast. Minimalistic example of derived class

#ifndef __GUN_CLUB_PLAYER_HPP__
#define __GUN_CLUB_PLAYER_HPP__

#include "Player.hpp"

class GunClubPlayer final: public Player
{
public:
    GunClubPlayer(size_t opponent = -1) : Player(opponent) {}

public:
    virtual Action fight()
    {
        return getTurn() % 2 ? bullet() : load();
    }
};

#endif // !__GUN_CLUB_PLAYER_HPP__

Answer 9

The PlasmaPlayer

The Plasma Player like firing his plasma bolts. He will try to load and fire as much as possible. However, while the opponent has plasma ammo, he will use his thermal shield (bullets are for the weak).

#ifndef __PLASMA_PLAYER_HPP__
#define __PLASMA_PLAYER_HPP__

#include "Player.hpp"

class PlasmaPlayer final : public Player
{
public:
    PlasmaPlayer(size_t opponent = -1) : Player(opponent) {}

    virtual Action fight()
    {
        // Imma Firin Mah Lazer!
        if (getAmmo() > 1) return plasma();

        // Imma Block Yur Lazer!
        if (getAmmoOpponent() > 1) return thermal();

        // Imma need more Lazer ammo
        return load();
    }
};

#endif // !__PLASMA_PLAYER_HPP__

Answer 10

The very SadisticShooter

He would rather watch you suffer than kill you. He's not stupid and will cover himself as required.

If you're utterly boring and predictable, he will just kill you straight off.

// SadisticShooter by muddyfish
// PPCG: http://codegolf.stackexchange.com/a/104947/11933

// SadisticShooter.hpp
// A very sad person. He likes to shoot people.

#ifndef __SAD_SHOOTER_PLAYER_HPP__
#define __SAD_SHOOTER_PLAYER_HPP__

#include <cstdlib>
#include "Player.hpp"
// #include <iostream>

class SadisticShooter final : public Player
{
public:
    SadisticShooter(size_t opponent = -1) : Player(opponent) {}
private:
    bool historySame(std::vector<Action> const &history, int elements) {
        if (history.size() < elements) return false;

        std::vector<Action> lastElements(history.end() - elements, history.end());

        for (Action const &action : lastElements)
            if (action != lastElements[0]) return false;
        return true;
    }
public:
    virtual Action fight()
    {
        int my_ammo = getAmmo();
        int opponent_ammo = getAmmoOpponent();
        int turn_number = getTurn();
        //std::cout << " :: Turn " << turn_number << " ammo: " << my_ammo << " oppo: " << opponent_ammo << std::endl;

        if (turn_number == 90) {
            // Getting impatient
            return load();
        }
        if (my_ammo == 0 && opponent_ammo == 0) {
            // It would be idiotic not to load here
            return load();
        }
        if (my_ammo >= 2 && historySame(getHistoryOpponent(), 3)) {
            if (getHistoryOpponent()[turn_number - 1] == THERMAL) return bullet();
            if (getHistoryOpponent()[turn_number - 1] == METAL) return thermal();
        }
        if (my_ammo < 2 && opponent_ammo == 1) {
            // I'd rather not die thank you very much
            return metal();
        }
        if (my_ammo == 1) {
            if (opponent_ammo == 0) {
                // You think I would just shoot you?
                return load();
            }
            if (turn_number == 2) {
                return thermal();
            }
            return bullet();
        }
        if (opponent_ammo >= 2) {
            // Your plasma weapon doesn't scare me
            return thermal();
        }
        if (my_ammo >= 2) {
            // 85% more bullet per bullet
            if (turn_number == 4) return bullet();
            return plasma();
        }
        // Just load the gun already
        return load();
    }
};

#endif // !__SAD_SHOOTER_PLAYER_HPP__

Answer 11

The TurtlePlayer

TurtlePlayer is a coward. He spends most of the time hiding behind his shields - hence the name. Sometimes, he may come out of his shell (no pun intended) and have a shot, but he normally he lies low whilst the enemy has ammo.

---

This bot is not particularly great - however, every KOTH needs some initial entries to get it running :)

Local testing found that this wins against both GunClubPlayer and Opportunist 100% of the time. A battle against BotRobotPlayer seemed to always result in a draw as both hide behind their shields.

#include "Player.hpp"

// For randomness:
#include <ctime>
#include <cstdlib>

class TurtlePlayer final : public Player {

public:
    TurtlePlayer(size_t opponent = -1) : Player(opponent) { srand(time(0)); }

public:
    virtual Action fight() {
        if (getAmmoOpponent() > 0) {
            // Beware! Opponent has ammo!

            if (rand() % 5 == 0 && getAmmo() > 0) 
                // YOLO it:
                return getAmmo() > 1 ? plasma() : bullet();

            // Play it safe:
            if (getAmmoOpponent() == 1) return metal();
            return rand() % 2 ? metal() : thermal();
        }

        if (getAmmo() == 0) 
            // Nobody has ammo: Time to load up.
            return load();

        else if (getAmmo() > 1) 
            // We have enough ammo for a plasma: fire it!
            return plasma();

        else 
            // Either load, or take a shot.
            return rand() % 2 ? load() : bullet();
    }
};

Answer 12

The DeceptivePlayer

The Deceptive Player tries to load two bullets and then fires one.

// DeceiverPlayer.hpp
// If we have two shoots, better shoot one by one

#ifndef __DECEPTIVE_PLAYER_HPP__
#define __DECEPTIVE_PLAYER_HPP__

#include "Player.hpp"

class DeceptivePlayer final: public Player
{
public:
    DeceptivePlayer(size_t opponent = -1) : Player(opponent) {}

public:
    virtual Action fight()
    {
        int ammo = getAmmo();
        int opponentAmmo = getAmmoOpponent();
        int turn = getTurn();

        // Without ammo, always load
        if (ammo == 0)
        {
            return load();
        }

        // Every 10 turns the Deceiver goes crazy
        if (turn % 10 || opponentAmmo >= 3)
        {
            // Generate random integer in [0, 5)
            int random = GetRandomInteger() % 5;
            switch (random)
            {
            case 0:
                return bullet();
            case 1:
                return metal();
            case 2:
                if (ammo == 1)
                {
                    return bullet();
                }

                return plasma();
            case 3:
                return thermal();
            case 4:
                return load();
            }
        }

        // The Deceiver shoots one bullet
        if (ammo == 2)
        {
            return bullet();
        }

        // Protect until we can get bullet 2
        if (opponentAmmo == 0)
        {
            return load();
        }

        if (opponentAmmo == 1)
        {
            return metal();
        }

        if (opponentAmmo == 2)
        {
            return thermal();
        }
    }
};

#endif // !__DECEPTIVE_PLAYER_HPP__

I do not code in c++ so any improvements to the code will be welcome.

Answer 13

HanSoloPlayer

Shoots first! Still working on revising it, but this is pretty good.

// HanSoloPlayer.hpp
// A reluctant rebel. Always shoots first.

// Revision 1: [13HanSoloPlayer][17] | 6 rounds | 2863

#ifndef __HAN_SOLO_PLAYER_HPP__
#define __HAN_SOLO_PLAYER_HPP__

#include "Player.hpp"

class HanSoloPlayer final: public Player
{
public:
    HanSoloPlayer(size_t opponent = -1) : Player(opponent) {}

public:
    virtual Action fight()
    {
        if(getTurn() == 0){
            // let's do some initial work
            agenda.push_back(bullet());     // action 2--han shot first!
            agenda.push_back(load());       // action 1--load a shot
        } else if(getTurn() == 2){
            randomDefensive();
        } else if(getRandomBool(2)){
            // go on the defensive about 1/3rd of the time
            randomDefensive();
        } else if(getRandomBool(5)){
            // all-out attack!
            if(getAmmo() == 0){
                // do nothing, let the agenda work its course
            } else if(getAmmo() == 1){
                // not quite all-out... :/
                agenda.push_back(load());   // overnext
                agenda.push_back(bullet()); // next
            } else if(getAmmo() == 2){
                agenda.push_back(load());   // overnext
                agenda.push_back(plasma()); // next
            } else {
                int ammoCopy = getAmmo();
                while(ammoCopy >= 2){
                    agenda.push_back(plasma());
                    ammoCopy -= 2;
                }
            }
        }

        // execute the next item on the agenda
        if(agenda.size() > 0){
            Action nextAction = agenda.back();
            agenda.pop_back();
            return nextAction;
        } else {
            agenda.push_back(getRandomBool() ? thermal() : bullet()); // overnext
            agenda.push_back(load());                                 // next
            return load();
        }
    }
private:
    std::vector<Action> agenda;
    bool getRandomBool(int weight = 1){
        return GetRandomInteger(weight) == 0;
    }
    void randomDefensive(){
        switch(getAmmoOpponent()){
            case 0:
                // they most likely loaded and fired. load, then metal shield
                agenda.push_back(metal());  // action 4
                agenda.push_back(load());   // action 3
                break;
            case 1:
                agenda.push_back(metal());
                break;
            case 2:
                agenda.push_back(getRandomBool() ? thermal() : metal());
                break;
            default:
                agenda.push_back(getRandomBool(2) ? metal() : thermal());
                break;
        }
        return;
    }
};

#endif // !__HAN_SOLO_PLAYER_HPP__

Answer 14

The CamtoPlayer

CamtoPlayer HATES draws and will break out of loops no matter what it takes. (except for suicide)

It's my first C++ program that does anything, so don't judge it too hard.

I know it could be better but please don't edit it.
If you want to modify the code just comment a suggestion.

#ifndef __CAMTO_HPP__
#define __CAMTO_HPP__

#include "Player.hpp"
#include <iostream>

class CamtoPlayer final : public Player
{
public:
    CamtoPlayer(size_t opponent = -1) : Player(opponent) {}
        int S = 1; // Switch between options. (like a randomness function without any randomness)
        bool ltb = false; // L.ast T.urn B.locked
        bool loop = false; // If there a loop going on.
        int histarray[10]={0,0,0,0,0,0,0,0,0,0}; // The last ten turns.
        int appears(int number) { // How many times a number appears(); in histarray, used for checking for infinite loops.
            int things = 0; // The amount of times the number appears(); is stored in things.
            for(int count = 0; count < 10; count++) { // For(every item in histarray) {if its the correct number increment thing}.
                if(histarray[count]==number) {things++;}
            }
            return things; // Return the result
        }
    virtual Action fight()
    {
        int ammo = getAmmo(); // Ammo count.
        int bad_ammo = getAmmoOpponent(); // Enemy ammo count.
        int turn = getTurn(); // Turn count.
        int pick = 0; // This turn's weapon.
        
        if(appears(2)>=4){loop=true;} // Simple loop detection
        if(appears(3)>=4){loop=true;} // by checking if
        if(appears(4)>=4){loop=true;} // any weapong is picked a lot
        if(appears(5)>=4){loop=true;} // except for load();
        
        if(ammo==0&&bad_ammo==1){pick=4;} // Block when he can shoot me.
        if(ammo==0&&bad_ammo>=2){S++;S%2?(pick=4):(pick=5);} // Block against whatever might come!
        if(ammo==0&&bad_ammo>=1&&ltb){pick=1;} // If L.ast T.urn B.locked, then reload instead.
        if(ammo==1&&bad_ammo==0){pick=2;} // Shoot when the opponent can't shoot.
        if(ammo==1&&bad_ammo==1){S++;S%2?(pick=2):(pick=4);} // No risk here.
        if(ammo==1&&bad_ammo>=2){S++;S%2?(pick=4):(pick=5);} // Block!
        if(ammo==1&&bad_ammo>=1&&ltb){pick=2;} // If ltb shoot instead.
        if(ammo>=2){S++;S%2?(pick=2):(pick=3);} // Shoot something!
        
        /* debugging
            std :: cout << "Turn data: turn: ";
            std :: cout << turn;
            std :: cout << " loop: ";
            std :: cout << loop;
            std :: cout << " ";
            std :: cout << "ltb: ";
            std :: cout << ltb;
            std :: cout << " ";
        */
        
        // Attempt to break out of the loop. (hoping there is one)
        if(ammo==0&&loop){pick=1;} // After many turns of waiting, just load();
        if(ammo==1&&bad_ammo==0&&loop){loop=false;pick=1;} // Get out of the loop by loading instead of shooting.
        if(ammo==1&&bad_ammo==1&&loop){loop=false;pick=4;} // Get out of the loop (hopefully) by blocking.
        if(ammo>=2&&loop){loop=false;S++;S%2?(pick=2):(pick=3);} // Just shoot.
        if(turn==3&&(appears(1)==2)&&(appears(2)==1)){pick=4;} // If it's just load();, shoot();, load(); then metal(); because it might be a loop.
        // End of loop breaking.
        
        if(turn==1){pick=2;} // Shoot right after reloading!
        if(ammo==0&&bad_ammo==0){pick=1;} // Always load when no one can shoot.
        
        for(int count = 0; count < 10; count++) {
            histarray[count]=histarray[count+1]; // Shift all values in histarray[] by 1.
        }
        histarray[9] = pick; // Add the picked weapon to end of histarray[].
        
        /*  more debugging
            std :: cout << "history: ";
            std :: cout << histarray[0];
            std :: cout << histarray[1];
            std :: cout << histarray[2];
            std :: cout << histarray[3];
            std :: cout << histarray[4];
            std :: cout << histarray[5];
            std :: cout << histarray[6];
            std :: cout << histarray[7];
            std :: cout << histarray[8];
            std :: cout << histarray[9];
            
            std :: cout << " pick, ammo, bammo: ";
            std :: cout << pick;
            std :: cout << " ";
            std :: cout << ammo;
            std :: cout << " ";
            std :: cout << bad_ammo;
            std :: cout << "\n";
        */
        switch(pick) {
            case 1:
                ltb = false; return load();
            case 2:
                ltb = false; return bullet();
            case 3:
                ltb = false; return plasma();
            case 4:
                ltb = true;return metal();
            case 5:
                ltb = true;return thermal();
        }
        
    }
};

#endif // !__CAMTO_HPP__

Answer 15

The SurvivorPlayer

The Survivor Player behaves in a similar vein as the Turtle and Barricade Player. He will never take an action that could lead to his death and would rather enforce a draw than to lose the fight.

// SurvivorPlayer.hpp
// Live to fight another day

#ifndef __SURVIVOR_PLAYER_HPP__
#define __SURVIVOR_PLAYER_HPP__

#include "Player.hpp"

class SurvivorPlayer final : public Player
{
public:
SurvivorPlayer(size_t opponent = -1) : Player(opponent)
{
}

public:
    virtual Action fight()
    {
        int myAmmo = getAmmo();
        int opponentAmmo = getAmmoOpponent();
        int turn = getTurn();
        if (turn == 0) {
            return load();
        }
        switch (opponentAmmo) {
        case 0:
            if (myAmmo > 2) {
                return GetRandomInteger(1) % 2 ? bullet() : plasma();
            }
            return load();
        case 1:
            if (myAmmo > 2) {
                return plasma();
            }
            return metal();
        default:
            if (myAmmo > 2) {
                return plasma();
            }
            return GetRandomInteger(1) % 2 ? metal() : thermal();
        }
    }
};

#endif // !__SURVIVOR_PLAYER_HPP__

Answer 16

The FatedPlayer

Made by Clotho, scored by Lachesis, and killed by Atropos; this player's only strategy is to use what it knows about ammo to determine which actions are reasonable.

However, it does not get to choose the action; that part is left to the gods.

#ifndef __FATEDPLAYER_H__
#define __FATEDPLAYER_H__

#include "Player.hpp"
#include <functional>
class FatedPlayer final : public Player
{
public:
   FatedPlayer(size_t o) : Player(o){}
   Action fight() {
      std::vector<std::function<Action()>>c{[&]{return load();}};
      switch(getAmmo()){
      default:c.push_back([&]{return plasma();});
      case 1 :c.push_back([&]{return bullet();});
      case 0 :;}
      switch(getAmmoOpponent()){
      default:c.push_back([&]{return thermal();});
      case 1 :c.push_back([&]{return metal();});
      case 0 :;}
      return c[GetRandomInteger(c.size()-1)]();
   }
};

#endif

...because I'd like to see how a random player ranks.

Answer 17

SpecificPlayer

SpecificPlayer follows a simple plan of choosing some random (valid) actions. However it's main feature is that it looks out for certain situations by analysing ammo counts and the opponent's previous move.

This is my first time writing anything in C++, and first time trying to do any sort of competitive bot writing. So I hope my meagre attempt at least does something interesting. :)

// SpecificPlayer by Charles Jackson (Dysnomian) -- 21/01/2017
// PPCG: http://codegolf.stackexchange.com/a/104933/11933

#ifndef __SPECIFIC_PLAYER_HPP__
#define __SPECIFIC_PLAYER_HPP__

#include "Player.hpp"

class SpecificPlayer final : public Player
{
public:
    SpecificPlayer(size_t opponent = -1) : Player(opponent) {}

    //override
    virtual Action fight()
    {
        returnval = load(); //this should always be overwritten

        // if both players have no ammo we of course load
        if (oa == 0 && ma == 0) { returnval = load(); }

        // if (opponent has increased their ammo to a point they can fire something) then shield from it
        else if (oa == 1 && op == LOAD) { returnval = metal(); }
        else if (oa == 2 && op == LOAD) { returnval = thermal(); }
        else if (op == LOAD) { returnval = randomBlock(oa); }

        // if we have a master plan to follow through on do so, unless a defensive measure above is deemed necessary
        else if (nextDefined) { returnval = next; nextDefined = false; }

        // if opponent didn't fire their first shot on the second turn (turn 1) then we should block
        else if (t == 2 && oa >= 1) { returnval = randomBlock(oa); }

        //if opponent may be doing two attacks in a row
        else if (oa == 1 && op == BULLET) { returnval = metal(); }
        else if (oa == 2 && op == PLASMA) { returnval = thermal(); }

        // if we had no ammo last turn and still don't, load
        else if (ma == 0 && pa == 0) { returnval = load(); }

        // if we have just collected enough ammo to plasma, wait a turn before firing
        else if (ma == 2 && pa == 1) { 
            returnval = randomBlock(oa); next = plasma(); nextDefined = true; }

        // time for some random actions
        else
        {
            int caseval = GetRandomInteger(4) % 3; //loading is less likely than attacking or blocking
            switch (caseval) 
            {
            case 0: returnval = randomBlock(oa); break; // 40%
            case 1: returnval = randomAttack(ma); break; // 40%
            case 2: returnval = load(); break; // 20%
            }
        }

        pa = ma; //update previous ammo then update our current ammo
        switch (returnval)
        {
        case LOAD:
            ma += 1;
            break;
        case BULLET:
            ma -= 1;
            break;
        case PLASMA:
            ma -= 2;
            break;
        }
        t++; //also increment turn counter

        return returnval;
    }

    //override
     void perceive(Action action)
    {
         //record what action opponent took and update their ammo
         op = action;
         switch (action)
         {
         case LOAD:
             oa += 1;
             break;
         case BULLET:
             oa -= 1;
             break;
         case PLASMA:
             oa -= 2;
             break;
         }
    }

private:
    Action returnval; //our action to return
    Action next; //the action we want to take next turn - no matter what!
    bool nextDefined = false; //flag for if we want to be taking the "next" action.
    int t = 0; //turn number
    int ma = 0; //my ammo
    int oa = 0; //opponent ammo
    int pa = 0; //my previous ammo
    Action op; //opponent previous action

    Action randomBlock(int oa)
    {
        Action a;
        if (oa == 0) { a = load(); }
        else if (oa == 1) { a = metal(); }
        else
        {
            // more chance of ordianry block than laser block
            a = GetRandomInteger(2) % 2 ? metal() : thermal();
        }
        return a;
    }

    Action randomAttack(int ma)
    {
        Action a;
        if (ma == 0) { a = load(); }
        else if (ma == 1) { a = bullet(); }
        else
        {
            // more chance of ordianry attack than plasma
            a = GetRandomInteger(2) % 2 ? bullet() : plasma();
        }
        return a;
    }
};

#endif // !__SPECIFIC_PLAYER_HPP__

Answer 18

NotSoPatientPlayer

The story of its creation will come later.

// NotSoPatientPlayer.hpp

#ifndef __NOT_SO_PATIENT_PLAYER_HPP__
#define __NOT_SO_PATIENT_PLAYER_HPP__

#include "Player.hpp"
#include <iostream>

class NotSoPatientPlayer final : public Player
{
    static const int TOTAL_PLAYERS = 50;
    static const int TOTAL_ACTIONS = 5;
    static const int MAX_TURNS = 100;
public:
    NotSoPatientPlayer(size_t opponent = -1) : Player(opponent)
    {
        this->opponent = opponent;
    }

public:
    virtual Action fight()
    {
        /*Part which is shamelessly copied from MontePlayer.*/
        int turn = getTurn(),
            ammo = getAmmo(),
            opponentAmmo = getAmmoOpponent();
        int turnsRemaining = MAX_TURNS - turn;
        //The bot starts to shoot when there is enough ammo to fire plasma at least (turnsRemaining-2) times.
        //Did you know that you cannot die when you shoot plasma?
        //Also chooses 1 or 2 move(s) in which will shoot bullet(s) or none if there is plenty of ammo.
        //Also check !burstMode because it needs to be done only once.
        if (!burstMode && ammo + 2 >= turnsRemaining * 2)
        {
            burstMode = true;
            if (!(ammo == turnsRemaining * 2)) {
                turnForBullet1 = GetRandomInteger(turnsRemaining - 1) + turn;
                if (ammo + 2 == turnsRemaining * 2) {
                    //turnForBullet1 should be excluded in range for turnForBullet2
                    turnForBullet2 = GetRandomInteger(turnsRemaining - 2) + turn;
                    if (turnForBullet2 >= turnForBullet1) turnForBullet2++;
                }
            }
        }
        if (burstMode) {
            if (turn == turnForBullet1 || turn == turnForBullet2) {
                return bullet();
            }
            else return plasma();
        }

        //if opponent defended last 3 turns, the bot tries to go with something different
        if (turn >= 3) {
            auto historyOpponent = getHistoryOpponent();
            //if opponent used metal last 3 turns
            if (METAL == historyOpponent[turn - 1] && METAL == historyOpponent[turn - 2] && METAL == historyOpponent[turn - 3]) {
                if (ammo >= 2) return plasma();
                else return load();
            }
            //if opponent used thermal last 3 turns
            if (THERMAL == historyOpponent[turn - 1] && THERMAL == historyOpponent[turn - 2] && THERMAL == historyOpponent[turn - 3]) {
                if (ammo >= 1) return bullet();
                else return load();
            }
            //if the opponent defends, but not consistently
            if ((historyOpponent[turn - 1] == METAL || historyOpponent[turn - 1] == THERMAL)
                && (historyOpponent[turn - 2] == METAL || historyOpponent[turn - 2] == THERMAL)
                && (historyOpponent[turn - 3] == METAL || historyOpponent[turn - 3] == THERMAL)) {
                if (ammo >= 2) return plasma();
                else if (ammo == 1) return bullet();
                else return load();
            }
        }

        /*else*/ {
            if (opponentAmmo == 0) return load();
            if (opponentAmmo == 1) return metal();
            //if opponent prefers bullets or plasmas, choose the appropriate defence
            if (opponentMoves[opponent][BULLET] * 2 >= opponentMoves[opponent][PLASMA]) return metal();
            else return thermal();
        }
    }

    virtual void perceive(Action action)
    {
        Player::perceive(action);
        opponentMoves[opponent][action]++;
    }

    /*virtual void declared(Result result)
    {
        currentRoundResults[opponent][result]++;
        totalResults[opponent][result]++;
        int duels = 0;
        for (int i = 0; i < 3; i++) duels += currentRoundResults[opponent][i];
        if (duels == 100) {
            std::cout << "Score against P" << opponent << ": " <<
                currentRoundResults[opponent][WIN] << "-" << currentRoundResults[opponent][DRAW] << "-" << currentRoundResults[opponent][LOSS] << "\n";
            for (int i = 0; i < 3; i++) currentRoundResults[opponent][i] = 0;
        }
    };*/

private:
    static long opponentMoves[TOTAL_PLAYERS][TOTAL_ACTIONS];
    int opponent;
    //When it becomes true, the bot starts shooting.
    bool burstMode = false;
    //turnForBullet1 and turnForBullet2,
    //the 2 turns in which the bot will shoot bullets
    int turnForBullet1 = -1, turnForBullet2 = -1;
    //For debugging purposes
    //Reminder: enum Result { DRAW, WIN, LOSS };
    static int currentRoundResults[TOTAL_PLAYERS][3], totalResults[TOTAL_PLAYERS][3];
};
long NotSoPatientPlayer::opponentMoves[TOTAL_PLAYERS][TOTAL_ACTIONS] = { { 0 } };
int NotSoPatientPlayer::currentRoundResults[TOTAL_PLAYERS][3] = { { 0 } };
int NotSoPatientPlayer::totalResults[TOTAL_PLAYERS][3] = { { 0 } };
#endif // !__NOT_SO_PATIENT_PLAYER_HPP__