Sudoku solver branch and bound

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;
+}