Instantly share code, notes, and snippets.

Last active May 23, 2024 13:46
Show Gist options
• Save p01/1230481 to your computer and use it in GitHub Desktop.
Sudoku Solver in 140bytes

# Sudoku Solver in 140 bytes

Solve a Sudoku grid only using magic, recursion, and 140bytes of brute force.

This entry was inspired and built on top of the itsy bitsy shoulders of the smallest sudoku solvers in Perl (120b), Ruby (122b), Python (178b), ...

Credits go this way:

``````166b @p01 .......... initial implementation
147b @p01 .......... initial golf
146b @qfox ......... loop optimization
145b @qfox ......... output with closured callback
140b @p01 .......... output with hijacked Array.prototype.toString()
141b @maksverver ... fixed the glitchy j^i==j test
140b @fgnass ....... ReferenceError exit trick + cross browser fix
``````

Thanks to everyone who helped golf and fix this puppy.

This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters. Learn more about bidirectional Unicode characters
 // /!\ WARNING this function assumes that there is no variable 'A' in the global scope function R ( a, // the array representing the sudoku grid // placeholder arguments i, // index of the last empty cell j, // index to check the candidates for the cell 'i' m, // candidate number for the the cell 'i' g // flag whether 'm' is a already used in the same row|col|node as 'i' ){ // phase 1: look for an empty cell for ( i=80; a[i]; // keep going if the cell isn't empty i--||A // decrease the index and throw a ReferenceError exception if we went through the whole grid ); // phase 2: check all candidate numbers for the cell 'i' for ( m=10; g=a[i]=--m; // put the candidate in the cell 'i' already and set 'g' to something truthy // at the end of phase 2, the cell 'i' is reset to 0 for "higher" branches of the recursion g&&R(a) // recurse if 'm' isn't already used in the same row|col|node as 'i' ) // phase 3: check if the candidate number is used already for(j in a) // loop through the whole grid again g*= // j==i // keep 'g' as is if we are on the cell 'i' || // otherwise, turn 'g' falsy if a[j]^m // the cell 'j' is set to 'm' || // and 'i' and 'j' are in the same row|col|node i%9^j%9&&i/9^j/9&&i/27^j/27|i%9/3^j%9/3 }
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters. Learn more about bidirectional Unicode characters
 function R(a,i,j,m,g){for(i=80;a[i];i--||A);for(m=10;g=a[i]=--m;g&&R(a))for(j in a)g*=j==i||a[j]^m||i%9^j%9&&i/9^j/9&&i/27^j/27|i%9/3^j%9/3}
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters. Learn more about bidirectional Unicode characters
 DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE Version 2, December 2004 Copyright (C) 2011 Mathieu 'p01' Henri - http://www.p01.org/releases/ Everyone is permitted to copy and distribute verbatim or modified copies of this license document, and changing it is allowed as long as the name is changed. DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION 0. You just DO WHAT THE FUCK YOU WANT TO.
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters. Learn more about bidirectional Unicode characters
 { "name": "sudokuSolver", "description": "Brute force sudoku solver.", "keywords": [ "sudoku", "solver", "recursive", "brute force" ] }
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters. Learn more about bidirectional Unicode characters
 Sudoku Solver in 140bytes

Sudoku Solver in 140bytes

Input value:

Expected value: 4,2,8,1,5,9,6,7,3,1,9,6,3,7,4,8,2,5,3,7,5,8,6,2,9,4,1,9,8,1,4,2,3,5,6,7,5,6,4,7,1,8,3,9,2,7,3,2,5,9,6,1,8,4,2,4,3,6,8,1,7,5,9,6,1,7,9,4,5,2,3,8,8,5,9,2,3,7,4,1,6

Actual value:

### jed commented Sep 21, 2011

this is just incredible.

### wjcrowcroft commented Sep 21, 2011

You people amaze me... +100 for the commented code!

Very nice.

### atk commented Sep 22, 2011

ES5 indexOf could save us 1 byte:
`function R(a,f,i,j,m,g){for(i=a.indexOf(0),~i||f(),m=10;g=a[i]=--m;g&&R(a,f))for(j in a)g*=a[j^i==j]^m||i/9^j/9&&i%9^j%9&&i/27^j/27|i%9/3^j%9/3}`

### christopherdebeer commented Sep 22, 2011

@p01 Out of curiosity (related to a side project I'm working on) - what would happen if the grid provided had no solution?

ie: If it fell out-with of the 6,670,903,752,021,072,936,960 possible permutations

Would it be easy enough to return false, or something to that effect?

### atk commented Sep 23, 2011

The number of actual calculated permutations is already reduced by the number of zeros in the input array; anyway, can a solution not be found, it would enter an infinite loop as at least one zero in the field cannot be cleared up.

### p01 commented Sep 27, 2011

I must say I find the closure thing wonky. Calling `myFunction(a,f);` which in turn calls `f` with no arguments just feel strange to me.

### p01 commented Sep 27, 2011

So I was thinking why not simply use the `.toString` method of the array to output the grid, and ... Boom! We have a winner!

140 bytes

`function R(a,i,j,m,g){for(i=80;a[i];i--||+a);for(m=10;g=a[i]=--m;g&&R(a))for(j in a)g*=a[j^i==j]^m||i/9^j/9&&i%9^j%9&&i/27^j/27|i%9/3^j%9/3}`

### pvdz commented Sep 27, 2011

Sleepy again? Why +a? Without checking further, either you meant ++a or the ||+a is completely useless...

### cjcliffe commented Sep 27, 2011

@qfox +a is just invoking a.toString(), not intended as an increment.

### jed commented Sep 27, 2011

the example doesn't work anymore, unfortunately.

### pvdz commented Sep 27, 2011

@cjcliffe I understand, but it's in the third part of the for statement, who's return-value is discarded. Hence, useless, because the toString has no notable side effects. At least none in this code.

### cjcliffe commented Sep 27, 2011

@qfox ah, how I was reading I assumed it would just set `a` to `a.toString()` when `i` reached 0 (when the || condition would trigger it)

### p01 commented Sep 28, 2011

Sorry for the broken example guys. Fixed now.

Yes `+a` does invoke `.toString()` here when `i` is equal to 0 and the cell #0 was not empty.

### jed commented Sep 28, 2011

hey @p01, can you figure out why it works in firefox and not in chrome? if indeed you golfed it down to a reliably working 140, that would be HUGE.

### p01 commented Sep 28, 2011

It does work in Opera and Firefox.

I'll try to figure what is going with the other browsers... if my baby girl "let" me, Priorities.
Meanwhile any help is appreciated.

### atk commented Sep 28, 2011

Chrome/V8 is somewhat critical on having his prototypes overwritten. Perhaps we can do with an object looking like an array and having a toString property? like in

``````testSudoku=[0,0,0,1,5,0,0,7,0,1,0,6,0,0,0,8,2,0,3,0,0,8,6,0,0,4,0,9,0,0,4,0,0,5,6,7,0,0,4,7,0,8,3,0,0,7,3,2,0,0,6,0,0,4,0,4,0,0,8,1,0,0,9,0,1,7,0,0,0,2,0,8,0,5,0,0,3,7,0,0,0];
for(var sudoku={toString:function(){ document.getElementById( "ret" ).textContent=... }},s=0,t=testSudoku.length;s<t;s++)sudoku[s]=testSudoku[s];
``````

### fgnass commented Sep 28, 2011

Here's another (maybe a little less dirty) approach that raises an error in order to stop the recursion. Hence the invocation has to be wrapped inside a try/catch block: https://gist.github.com/1247640

### p01 commented Sep 28, 2011

Nice moves!

@fgnass: Clever (ab)use of a ReferenceError. Before even using a callback method I tried a similar but more expensive approach with `throw a`

### jspillers commented Sep 28, 2011

Bravo sir, bravo.

### whichsteveyp commented Sep 28, 2011

I want to be like you when I grow up.

### lrvick commented Sep 28, 2011

You make me happy.

This is awesome.

### maksverver commented Sep 29, 2011

Just a notification: as I wrote on on Reddit the current version of the code is buggy. (See the linked post for details and a solution.)

### p01 commented Sep 29, 2011

Finally someone managed to reproduce this glitch. I tried the exact fix you suggested a few days ago: It works, unfortunately it is one byte bigger ( not smaller ), which bring us back to 141 bytes. One byte too many for 140byt.es

But I'm sure we can golf a valid version down to 140 bytes.

### pvdz commented Sep 29, 2011

Oh, I only see now that you're adding sugar for the `toString` "callback" in the test. I hadn't seen that before, just read the comments. That's why I was confused by the `||+a` part. If you modify `toString`, the rules obviously change.

So I can see what you mean, but do you think this would be possible or acceptable in a js1k? I'd think the (temporary) `toString` modification is boiler plate, but still required for the solution. Guess what I'm asking is, do you really think this is a proper 140b entry, or should the toString modification actually kind of be part of it. Especially when golfing, I think it matters. And I think it does. Just my two cents... :)

### p01 commented Sep 29, 2011

The `toString` sugar would definitely count in a JS1K: Every thing counts in JS1K.

However things seem a more lax at 140byt.es. See the base64 entries for instance where the whole list of characters is passed as argument ( a whooping 64+ bytes for free ).

That being said, if people are OK with encapsulating the call in a `try/catch`, then we can settle this at 140 bytes with a mix of fgnass ReferenceError trick and maksverver decomposition of the test `i!=j && a[j]!=m`

### pvdz commented Sep 29, 2011

However things seem a more lax at 140byt.es. See the base64 entries for instance

Fair enough :)

### atk commented Sep 30, 2011

I agree, though I'd rather find a way to shorten up the calculation for 1 bit...