Wednesday, November 30, 2005

Sudoku Solver

This afternoon I wrote a sudoku solver in Prolog. I haven't written a Prolog programme since I was at university nearly ten years ago, so it's a bit of a brute force attack really. I tested it on small grids to start with and it worked ok, but on a full sudoku so far it's taken three hundred and ninety-eight minutes and hasn't returned a result. I'll leave it going overnight, but if it hasn't worked it out by morning I'm giving up. Since I have no desire to learn how to code in Prolog properly. I could probably write something in Java to solve it in a few seconds. (That is, the solving would take a few seconds, not the writing.)


Philip Rodrigues said...

Heh, exactly the reason why I've never attempted a sudoku and don't plan to. Why waste brain power on an exercise in combinatorics when a script can do it? Cryptic crosswords all the way! :-)

quakegamer said...

quick solution, caml

open Facile;;
open Easy;;

let print queens =
let n = 9 in
for i = 0 to n - 1 do
for j = 0 to n - 1 do
let c = Fd.int_value queens.(9*i+j) in
Printf.printf "%d " c
print_newline ()
flush stdout;;

let puzzle = [|
5; 3; 0; 0; 7; 0; 0; 0; 0;
6; 0; 0; 1; 9; 5; 0; 0; 0;
0; 9; 8; 0; 0; 0; 0; 6; 0;

8; 0; 0; 0; 6; 0; 0; 0; 3;
4; 0; 0; 8; 0; 3; 0; 0; 1;
7; 0; 0; 0; 2; 0; 0; 0; 6;

0; 6; 0; 0; 0; 0; 2; 8; 0;
0; 0; 0; 4; 1; 9; 0; 0; 5;
0; 0; 0; 0; 8; 0; 0; 7; 9;
let myarr = Fd.array 81 1 9;;

for i=0 to 80 do
let value = Array.get puzzle i in
if value > 0 then (fd2e myarr.(i) =~ i2e value);

(* constraints horizontal, vertical and squares *)
let chooser i x y =
if i=0 then x*9+y
else if i=1 then x+y*9
else (27*(x/3)+3*(x mod 3)) + (9*(y/3)+(y mod 3))

(* add the constraints *)
for c=0 to 2 do
for i=0 to 8 do
let arr = Array.init 9 (fun k -> myarr.(chooser c i k)) in (Alldiff.cstr arr)

(* solve *)
let goal = Goals.GlArray.labeling myarr in
if (Goals.solve goal) then print myarr
else failwith "no solution found"

Reviewer said...

The fun of Sudoku is for the human mind to solve it, the individual confrontation. On this website, Sudoku Daily at you can select the type of game and store a game that is half-finished. It looks good too.

Jonathan said...

Interesting :)

I also wrote a solver. It is free and it is online here. No need to download and install anything. All you need is your browser. You'll see, it is very easy to use and very fast. It will also tell you if there are more than one solution for your sudoku.

Here is the link again: ]Good Camel's Sudoku Solver!

Happy Sudoku :)

Dany Gunawan said...

Hi all..
I've just also finished developing my sudoku solver.
I've posted it online on

I wrote it in .NET language and I think it quite fast too as it takes more intelligent checking instead of having to do any time-consumed brute force :)

You're more than welcome to visit it at anytime guys heheheeeee

Viva Sudoku said...

Here is one solver it solves everything but takes a few seconds in some cases.

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