Lambda the Ultimate

I have a sudoku program on my phone, and it can calculate a solution. My guess is that the solution isn't unique and that a solver that assumes a unique solution might not find one.

Your solver has a bug. (See the result of your example!)

if ( s[a][b][x][y] == j || s[a][x][c][y] == j || s[x][y][c][d] == j )

should be

if ( s[a][b][x][y] == j || s[a][x][c][y] == j || s[x][b][y][d] == j )

Ah, thanks for the fix. When I run it now I get this answer:

 2 3 9 | 5 4 8 | 6 7 1
 4 7 1 | 2 6 9 | 8 5 3
 6 8 5 | 3 7 1 | 4 2 9
-------+-------+-------
 5 1 6 | 7 8 3 | 9 4 2
 8 9 2 | 1 5 4 | 3 6 7
 3 4 7 | 6 9 2 | 1 8 5
-------+-------+-------
 1 6 4 | 9 2 5 | 7 3 8
 7 2 3 | 8 1 6 | 5 9 4
 9 5 8 | 4 3 7 | 2 1 6

You could change your program to let it show all possible solutions. (Something like replacing return true with display(); return false)

Yes, that's what I did first. This even makes the program smaller as I don't need to worry about returning values. The problem with this however was that in cases where there are a lot of solutions it was crashing my browser. I guess that JavaScript really isn't the ideal language for this type of program. I should have written it in Java or C (it is practically identical anyway) but I actually wrote it as an exercise for learning JavaScript (it is my first JS program).