Program to solve Sudoku Puzzles written in F# The solver is efficient in the places that count and solves "hard" sudoku puzzles in no more than 60 secs. The solver uses multiple cores to search for a solution and only very rarely spends more than a second on a solution. Input is a file like this: 003020600 900305001 001806400 008102900 700000008 006708200 002609500 800203009 005010300 where 0 means the square is open. (Used on Project Euler) Or like this: ..3.2.6..9..3.5..1..18.64....81.29..7.......8..67.82....26.95..8..2.3..9..5.1.3.. where "." means the square is open. This is what is most commonly used. Put your soduku square in the test.sdk file and go The sample above is taken from http://projecteuler.net/index.php?section=problems&id=96 Some "hard" problems are found on http://en.wikipedia.org/wiki/Algorithmics_of_sudoku. The sudoku problem in test.sdk is from there under the label "golden nugget" I used http://www.sudoku-solutions.com/ to find and check solutions too.