From 80c974b2917116079c4354f85e0d6a0c91d239c3 Mon Sep 17 00:00:00 2001
From: Valentin Gehrke <madmaurice@zom.bi>
Date: Tue, 23 Feb 2016 12:39:41 +0100
Subject: [PATCH] Sudoku solver branch and bound
---
sudoku.c | 87 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 87 insertions(+)
create mode 100644 sudoku.c
diff --git a/sudoku.c b/sudoku.c
new file mode 100644
index 0000000..fd34d74
--- /dev/null
+++ b/sudoku.c
@@ -0,0 +1,87 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+typedef char Sudoku[81];
+typedef enum { true, false } bool;
+
+bool* get_possible_solutions(Sudoku s, int row, int col) {
+ bool* solutions = malloc(sizeof(bool)*10);
+
+ for(int i = 0; i < 10; i++) solutions[i] = true;
+
+ for(int ccol = 0; ccol < 9; ccol++)
+ solutions[ s[row*9+ccol] ] = false;
+
+ for(int crow = 0; crow < 9; crow++)
+ solutions[ s[crow*9+col] ] = false;
+
+ for(int crow = row - row%3, rsteps = 0; rsteps < 3; crow++, rsteps++) {
+ for(int ccol = col - col%3, csteps = 0; csteps < 3; ccol++, csteps++) {
+ solutions[ s[crow*9 + ccol] ] = false;
+
+ }
+ }
+
+ return solutions;
+}
+
+int sudoku_solve_rec(Sudoku s, int row, int col) {
+ if(row >= 9)
+ return 1;
+ if(col >= 9)
+ return sudoku_solve_rec(s, row + 1, 0);
+
+ if(s[row*9+col] != 0)
+ return sudoku_solve_rec(s, row, col + 1);
+
+ bool* solutions = get_possible_solutions(s, row, col);
+
+ for(int solution = 1; solution <= 9; solution++) {
+ if(solutions[solution] == false) continue;
+ s[row*9+col] = solution;
+ if(sudoku_solve_rec(s, row, col + 1)) {
+ free(solutions);
+ return 1;
+ }
+ }
+
+ s[row*9+col] = 0;
+
+ free(solutions);
+
+ return 0;
+}
+
+int sudoku_solve(Sudoku s) {
+ return sudoku_solve_rec(s, 0,0);
+}
+
+int main( int argc, char *argv[] ) {
+
+ Sudoku s = {
+ 0,3,0,0,0,0,0,0,0,
+ 0,0,0,1,9,5,0,0,0,
+ 0,0,8,0,0,0,0,6,0,
+ 8,0,0,0,6,0,0,0,0,
+ 4,0,0,8,0,0,0,0,1,
+ 0,0,0,0,2,0,0,0,0,
+ 0,6,0,0,0,0,2,8,0,
+ 0,0,0,4,1,9,0,0,5,
+ 0,0,0,0,0,0,0,7,0
+ };
+
+ if(sudoku_solve(s)) {
+ printf("Solved\n");
+ } else {
+ printf("Not solved\n");
+ }
+
+ for(int row = 0; row < 9; row++) {
+ for(int col = 0; col < 9; col++) {
+ printf("%d ",s[row*9+col]);
+ }
+ printf("\n");
+ }
+
+ return 0;
+}