Crack the code to the combination lock

Question

Given a standard combination lock like the one in the picture. The way to unlock it is to align the 4 numbers in the code on the combination line. After years of loyal service you have been fired from the lock factory and have decided to exact revenge by not jumbling up the locks before you send them off, thus leaving every lock with the combination to unlock it on the combination line.

You also know that by looking at the order of the numbers in the other lines it is possible to work out what numbers must be on the combination line (and therefore the combination to unlock it is).

If every line on the lock is given a number starting from line 0 for the combination line (the line which unlocks the lock) to line 9. For example, if the numbers on line 4 are 5336, then the combination to unlock it would be 1992.

Unfortunately the locks have already been packaged and your view of each lock is obscured, so you can only see numbers on different lines of the lock.

The Challenge

Given 4 pairs of digits, where the first digit of the integer represents the line number and the second digit represents the the number which appears on that line, work out the combination to the lock. For example if you input:

57 23 99 45

Then it should output:

2101

Or

25 78 63 15

and

3174

Assume the input will always be 4 positive integers in the form `25 64 72 18.

This is code-golf, so the shortest programs in number of bytes wins.

Also this is my first question, so any feedback is appreciated.

Answer 1

CJam, 9 8 bytes

ea9fbAf%

Reads the digit pairs as command-line arguments. To try the code online, change ea to lS/ to read from simulated STDIN.

Example run

$ cjam <(echo ea9fbAf%) 57 23 99 45; echo
2101
$ cjam <(echo ea9fbAf%) 25 78 63 15; echo
3174

How it works

The character code of the digit d is 48 + d. Thus, considering the two-digit string xy a base 9 number yields 9 * (48 + x) + (48 + y) = 10 * (48 + x) + y - x ≡ y - x (mod 10).

ea       " Push the array of command-line arguments.                                      ";
  9fb    " Mapped base 9 conversion; replace each string 'xy' with (9 * ord(x) + ord(y)). ";
     Af% " Take the results modulo 10.                                                    ";

Answer 2

CJam, 13 12 11 characters

Thanks to user23013, its now down to 11 characters :)

4{Ar:--A%}*

Explanations:

4{       }*     "Run the code block 4 times";
   r            "Read the next input token (whitespace separated)";
    :-          "Subtract 2nd number from the first treating r as a 2 numbered string";
  A   -         "Subtract the result of above from 10";
       A%       "Take modulus of 10 and store it on stack";

Try it online

I know it can be golfed more. But this is my first real attempt on CJam and I am limited by experience :)

---

Alternatively, the other methods to do the same thing in 1 extra character:

l~]{_A/-A%}/     // My previous solution

or

4{ri_A/-A%}*     // As pointed out by Ingo

or

ea{i_A/-A%}/     // If input is passed through command line

Answer 3

Golfscript (14 13)

Try it online here

It's pretty much the same as Optimizer's solution, but in a different language. It's hard to approach it in a different way because the problem is fairly simple, so the tie definitely goes to Optimizer, whose entry was earlier anyway.

~]{.10:^/-^%}/

For the same number of bytes you can do

~]{.10/- 10%}/

Answer 4

GNU dc, 14 bytes

Borrowing @Dennis's clever base 9 trick:

9i[?A%nd]dxxxx

Input integers read from STDIN, one per line.

Explanation:

9i                # Set input radix to 9
  [     ]         # push a macro, defined thus:
   ?              #   read number from STDIN and push
    A             #   push literal 10
     %            #   calculate number mod 10
      n           #   print, with no newline
       d          #   duplicate macro
         d        # duplicate macro
          xxxx    # execute the macro 4 times    

Output:

$ for i in 57 23 99 45; do echo $i; done | dc ./combolock.dc
2101$ 
$ for i in 25 78 63 15; do echo $i; done | dc ./combolock.dc
3174$ 
$ 

---

Previous Answer, 18 bytes:

Because I thought I could get closer to the "golfing" languages with this (but didn't):

[A?A~--A%n]dddxxxx

Answer 5

C 64 63 56 or 61

If the input can be piped from file

main(a){while(scanf("%d",&a)>0)putchar(48+(a-a/10)%10);}

If the input should be typed to stdin

i;main(a){for(;i++-4;putchar(48+(a-a/10)%10))scanf("%d",&a);}

Reads the four numbers in a loop and then processes each by subtracting the first digit from the value and printing the result modulo 10.

Savings thanks to various comments below and also using putchar instead of printf

Answer 6

Python 3 , 64

Straightforward.

print(''.join([(i-i//10)%10 for i in map(int,input().split())]))

It can be shorter if I'm allowed to print, say, [2, 1, 0, 1] instead (46):

print([i%10-i//10 for i in map(int,input().split())])

Answer 7

C, 92

#define a(n) ,(10+v[n][1]-*v[n])%10
main(int c,char**v){printf("%d%d%d%d"a(1)a(2)a(3)a(4));}

Input from commandline. Subtracts the first ASCII code of each argument from the second, adds 10 and takes modulo 10.

I think this is the first time I've written a printf with four %s and no comma (the comma is in the #define.)

Answer 8

Java - 203 bytes

Just because there has to be a Java entry, I saw a nice opportunity to give this code golfing a chance (first submission ever).

class M{public static void main(String[] a){String r="";for(int i=0;i<4;i++){int l=Byte.valueOf(a[i].substring(1));int f=Byte.valueOf(a[i].substring(0,1));r+=(l-f<0)?l-f+10:l-f;}System.out.print(r);}}

If there's room for some improvements, I'd glad to know about them ;-)

Answer 9

Lua - 46 characters

while''do a,b=io.read(1,1,1)print((b-a)%10)end

Reads three characters at a time (grant me the small mercy of inputing a space at the end), and eventhough a and b are string-y... b-a MAGICALUALY allows them to conceive a healthy baby integer. Does the wrap-around check while printing.

Answer 10

JavaScript ES6 – 53 43 bytes

f=n=>n.replace(/.. ?/g,a=>(1+a[1]-a[0])%10)

Fairly straightforward function, uses regex to get the numbers. Try it out at http://jsfiddle.net/efc93986/1/. If functions are not allowed, a standalone program at 52 bytes:

alert(prompt().replace(/.. ?/g,a=>(1+a[1]-a[0])%10))

As ES6 currently only works on Firefox, the following code works on any modern browser, at 70 bytes:

alert(prompt().replace(/.. ?/g,function(a){return(1+a[1]-a[0])%10}))

Answer 11

Python 2 - 33 bytes

for i in input():print(i-i/10)%10

Accepts comma-delimited user input. E.g. Input:

29,26, 31, 88

Output:

7
4
8
0

If output is required to exactly match the example then it is much longer. 47 bytes:

print"%d"*4%tuple((i-i/10)%10 for i in input())

Answer 12

APL, 14

10|{--/⍎¨⍕⍵}¨⎕

Explaination
⎕ takes input from screen. Space-separated values are parsed as an array.
{...}¨ for each number, feed it into function.
⍎¨⍕⍵ takes the argument, create an array of its digits.
--/ calculates units minus tens.
10| mod 10.

Answer 13

J - 20 15

The non-verb form (as statement instead of function definition) it's 5 characters shorter:

10|-~/|:10#.inv

The verb form which is a nice train:

10|[:-~/[:|:10#.inv]

This verb used on the example inputs:

   10|-~/|:10#.inv 57 23 99 45
2 1 0 1
   10|-~/|:10#.inv 25 78 63 15
3 1 7 4

rotd =: 10|[:-~/[:|:10#.inv] NB. verb form

   rotd 25 78 63 15
3 1 7 4
   rotd 57 23 99 45
2 1 0 1

Answer 14

Haskell 60 58

main=interact$show.map((\x->mod(x-x`div`10)10).read).words

Single character digits, a real nemesis in Haskell golfing.

Answer 15

Perl: 38 40

print abs($_-int$_/10)%10for split" ",<>

Output:

% perl code.pl
57 23 99 45
2101

25 78 63 15                                     
3174

Answer 16

Ruby, 35 bytes

$*.map{|n|a,b=n.bytes;$><<(b-a)%10}

Explanation

Input is taken as command line arguments. String#bytes returns an Array of Integers (ASCII character codes). Only the difference between the last and first character code is of importance, not the Integers themselves.

Answer 17

C# & LinqPad: 104

Util.ReadLine<string>("").Split(' ').Select(s =>(s[1]-s[0])).Aggregate("",(r,a)=>r+(a<0?10+a:a)).Dump();

Answer 18

C++ 118

int main()
{
int a,b,c;
for(int i=0; i<4; i++)
{
cin>>a;
b=a/10;
a=a%10;
c=a-b;
if(c<0)c+=10;
cout<<c;
}
}

Answer 19

PHP - 90 characters

Thought I'd give code golf a try so here it is, my first attempt - can probably be golfed more.

<?php $a=array(57,23,99,45);foreach($a as$b){echo abs(substr($b,0,1)-substr($b,1,1)%10);}

58 characters (courtesy of Ismael Miguel)

for($i=0,$a=$_GET[n];$i<8;)echo abs($a[$i++]-$a[$i++]);

Access file using

file.php?n=57239945

Answer 20

Python 3, 60

for x in input().split():print(-eval('-'.join(x))%10,end='')

Input and output exactly as specified, although it doesn't print a trailing newline. Two interesting tricks here: 1) replacing two calls to int() with one call to eval(), and 2) using join() to get a-b, then negating it for b-a as required. Fortunately Python's modulo operator gives positive values even if the first argument is negative!