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Troll league table

<script src="https://ajfaraday.github.io/Thud/dist/data/tables.js"></script><script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script><table> <thead> <tr> <th>Client</th> <th>Wins</th><th>Loses</th> <th>Score</th> </tr></thead> <tbody id="clients"> </tbody></table><script type='text/javascript'>  
league_table.troll.forEach( function(data_row){var row=$('<tr>'); var cell=$('<td>'); cell.html(data_row.name.substring(6)); row.append(cell); cell=$('<td>'); cell.html(data_row.win); row.append(cell); cell=$('<td>'); cell.html(data_row.lose); row.append(cell);row.append(cell);cell=$('<td>'); cell.html(data_row.score); row.append(cell); $('tbody#clients').append(row);});</script>

Thud is a game described by Terry Pratchett in his novel, Thud!

The game simulates a battle between the Dwarfs (in blue) and the Trolls (in green) on an octagonal board with the Thudstone (an impassable space) in the centre of the board.

Thud board in starting positions

I have created an environment to play the game and create your automated player at: https://ajfaraday.github.io/Thud/dist/index.html

The challenge is to write the most successful troll player of this game (these will be two separate challenges).


Starting with the dwarf player, players take it in turns to move.

Dwarf Movement

On the dwarf player's turn, they can move one dwarf piece either as a walk or a hurl.

Walk: Dwarfs can move as far as they like in any direction until they hit an obstacle (another dwarf, the edge of the board, or a troll). They can only kill a troll by walking if they are only one space away.

Hurl: If two or more dwarfs are in a line (horizontal, vertical or diagonal), they can hurl the dwarf on the end of the line, by the length of the line (e.g. in a line of 3, the dwarf on the end can be hurled 3 spaces). If a dwarf is hurled into a troll, the troll is killed, reducing the troll player's score by 4 points.

Troll Movement

On the Troll player's turn they can move one troll piece, either as a walk or a shove.

Walk: Trolls can move one space in any direction, unless a troll, dwarf or the edge of the board is in the way. Whenever a troll moves, it kills all dwarfs adjacent to its destination space.

Shove: If two or more trolls are in a line (horizontal, vertical or diagonal) they can shove the troll at the end of the line that number of spaces away, but only if any of the target space's immediate
neighbours contain a dwarf. When a troll is shoved, it kills all dwarfs on or adjacent to it's destination space.

A troll may not land directly on a dwarf by either walk or shove moves.

Each dwarf killed reduces the dwarf player's score by 1 point.


The score is calculated thus:

  • The dwarf player has one point for every dwarf remaining on the board.
  • The troll player has four points for every troll remaining on the board.
  • The key figure is the difference between these two. This will be used to calculate players' scores in the tournament.

Ending the game

The game ends when any of these conditions is met:

  • There are no dwarfs on the board.
  • There are no trolls on the board.
  • Both players have declared the game over.
  • The game has reached its cut-off length of 500 moves.

How to manually play a game

  • Go to https://ajfaraday.github.io/Thud/dist/index.html
  • Hover the mouse over a piece to see it's available moves.
  • Click on a piece to select it for the current move.
  • Click on one of the available moves to move the piece.
  • (You can click the relevant 'Make Peace' button to declare the game over according to that player, during their turn)

How to set up a local instance of the game

You don't have to clone the repository and use it locally to make the game work, or to create an entry, but it helps.

  • git clone https://github.com/AJFaraday/Thud.git
  • cd Thud
  • npm install
  • You can then call node script/get_clients.js to get the latest entries from Stack Exchange

If you prefer, you can use the github pages instance at https://ajfaraday.github.io/Thud/dist/index.html

How to customize a game

  • Open /dist/index.html in your browser
  • Click 'Customize'
  • Select troll and dwarf clients (manual allows direct control)
  • Select a turn time in milliseconds (only relevant to non-manual players)
  • Click 'Run Game' to see or play the game.
  • (Clicking 'Close' will not enact any changes)


The game is played by clients, which represent either a troll or a dwarf player. Each is a JavaScript class which must have these three functions:

  • constructor(controller) - controller is an object which acts as your interface with the game (see below).
  • turn() - This is called whenever it is your players turn to move.
  • end_turn() - This is called after your player's turn is over. It can not move pieces, but can make decisions on whether or not to declare the game over.


The controller object is your client's interface with the game itself. You can find full documentation for the controller class here: https://github.com/AJFaraday/Thud/blob/main/docs/controller_interface.md

It provides these functions to interrogate the state of the game:

  • turn() - Current turn of the game
  • scores() - The current score
  • spaces() - Every space, and what's in it
  • space_info(x, y) - Detailed information on any space on the board.
  • dwarfs() - The location of every dwarf
  • trolls() - The location of every troll
  • pieces() - All pieces belonging to the current player (equivalent of dwarfs() or trolls())
  • indexed_dwarfs() - The location of every dwarf with a fixed index
  • indexed_trolls() - The location of every troll with a fixed index
  • previous_move() - What got moved to where last turn
  • killing_moves() - All moves which can kill one or more opponent
  • current_space - Currently selected space (not a function)
  • clear_space() - Empties currently selected space

These functions are used to actually make your move:

  • check_space(x, y)- Find out what moves are available from a given space
  • select_space(x, y) - The player decides to move a piece at space.
  • check_move(x, y) - Find out what will happen if you move to a place
  • move(x, y) - The player moves the current piece to the selected space.

These are concerned with ending the game:

  • declare(game_over) - Say whether or not your player thinks the game is over.
  • opponent_declared() - Has the opponent declared the game over?

Your client will also have a utils object which will provide these helpful geometry functions:

  • utils.distance_between(source, target) - The square distance between two objects which respond to x and y
  • utils.farthest_from(spaces, target) - From an array of spaces (with x and y), choose the farthest from target (with x and y)
  • utils.closest_to(spaces, target) - From an array of spaces (with x and y), choose the closest to target (with x and y)

How to write a client

Warning: There is an issue with the project on Firefox (https://github.com/AJFaraday/Thud/issues/3) which prevents editing the code in the browser. This has been confirmed to work in Chrome.

  • Open 'dist/index.html' in your browser.
  • Click 'Customize'.
  • Select 'dwarf/template' as the Dwarf player (or use another client as a starting point).
  • Click 'Edit' beside the Dwarf player select.
  • Write your client code in the text box provided.
  • The Validate button will change colour based on whether or not the client is passes validations (see below).
  • When you're happy with it, click 'Apply' (This can be done before it passes validation, but it may not actually work).
  • Select a worthy opponent and click 'Run Game' to see the game.


In order for a client to work, and therefore be enterable in the challenge, it has to pass these validations:

  • It must evaluate as Javascript code.
  • The code must return a class with a constructor which accepts one argument.
  • Instances of this class should have functions named turn() and end_turn()
  • The client must play a game until it is over (i.e. it must call a valid move during every turn call). The validator will run games against default opponents to determine if this happens.
  • Does not have any forbidden terms
    • game. - Only interact with the game via controller
    • Math.random - Please keep it deterministic
    • setTimeout or setInterval - Keep it sequential
    • eval, require or import - Just don't

You can open the developer console (F12) to see more detailed information on your client's validation process.

How to save a client

If you have cloned the git repository, you can save your entry for future tinkering. This step is not required for entry in the challenge, but it may be helpful.

  • Edit a client, as above.
  • When you're happy with it (preferably if it's passing validation, too), click 'Copy' from the edit interface.
  • Create a .js file in /src/clients/dwarf/entry with the name of your entry e.g. /src/clients/dwarf/entrygreat_dwarf_player.js. (This folder will not be wiped by get_clients.js)
  • Run node script/get_clients.js from the Thud directory to make your entry available from the Dwarf player select. You only need to do this once to make it avilable.
  • npm run build - this will keep watching for changes in your entry and updating the package.

How to enter your client in the competition

  • Decide on the name of your client, your client_name must only have alpha characters and underscores.
  • Answer this question with your entry
    • The first line of your answer should be your client's name as a title (with = characters under it on the second line)
    • There should be a code block containing the class for your entry (with or without the preceeding module.exports =)
    • After that please include a brief explanation of your client's behaviour, and any other information you'd like to include.

Once this is in place, anyone running ./get_answers.sh will see your client available under your username.

The GitHub Pages instance will also be updated periodically, so by making an entry, your code will be added to the repo.

Tournament rules

The tournament will pit every available dwarf client (in /src/clients/dwarf/) against every available troll client (in /src/clients/troll/), and each pairing will play exactly one game.

The difference between the two players' scores will then update a running total for each client. The winner will gain the difference, and the loser will lose the difference.

There are two winners in the tournament: the most successful troll player and the most successful dwarf player.

Seeing the result of the tournament

You can use the 'League Table' button to see the overall results of the clients. If you click on a client, you will see all the matches for that client.

You can use the 'Matches' button to see the result of all matches. If you click on a match, the game will replay the match for you. You can change the select at the bottom of the screen to highlight specific clients.

To rerun the tournament (including changes on Stack Exchange and your own entries in /src/clients/dwarf/entry) you can run .get_answers.sh. This will update the 'League Table' and 'Matches' screens.

According to the rules, after playing a game, the players swap sides, so please also write an entry on the dwarf challenge.



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