Sudoku solver

sudoku.c

#include <stdio.h>
#define ORDER 3
#define DIM ORDER*ORDER

int checkLine(int m[DIM][DIM], int line)
{
    int i, j;
    for (i = 0; i < DIM-1; i++)
        for (j = i+1; j < DIM; j++)
            if (m[line][i] == m[line][j] &&
                m[line][i] > 0)
                return 0;
    return 1;
}

int checkColumn(int m[DIM][DIM], int column)
{
    int i, j;
    for (i = 0; i < DIM-1; i++)
        for (j = i+1; j < DIM; j++)
            if (m[i][column] == m[j][column] &&
                m[i][column] > 0)
                return 0;
    return 1;
}

int checkSub(int m[DIM][DIM], int r, int c)
{
    int v[DIM], i, j, k=0;
    for (i = r; i < r+ORDER; i++)
        for (j = c; j < c+ORDER; j++) {
            v[k] = m[i][j];
            k++;
        }
    for (i = 0; i < DIM; i++)
        for (j = i+1; j < DIM; j++)
            if (v[i] == v[j] && v[i] > 0)
                return 0;
    return 1;
}

int checkSubMatrix(int m[DIM][DIM])
{
    int r, c;
    for (r = 0; r < DIM; r += ORDER)
        for (c = 0; c < DIM; c += ORDER)
            if (checkSub(m, r, c)==0)
                return 0;
    return 1;
}

int checkGame(int m[DIM][DIM])
{
    int i;
    for (i = 0; i < DIM; i++)
        if (checkLine(m, i) == 0   ||
            checkColumn(m, i) == 0 ||
            checkSubMatrix(m) == 0  )
            return 0;
    return 1;
}

void printMatrix(int m[DIM][DIM])
{
    int i, j;
    for (i = 0; i < DIM; i++) {
        for (j = 0; j < DIM; j++)
            printf("%i\t", m[i][j]);
    printf("\n");
    }
}

int complete(int m[DIM][DIM], int *x, int *y)
{
    int i, j;
    for (i = 0; i < DIM; i++)
        for (j = 0; j < DIM; j++)
            if (m[i][j] == 0) {
                *x = i;
                *y = j;
                return 0;
            }
    return 1;
}

int solveGame(int m[DIM][DIM])
{
    int x, y, i;
    if (checkGame(m) == 0)
        return 0;
    if (complete(m, &x, &y) == 1) {
        if (checkGame(m) == 0)
            return 0;
        else
            return 1;
    }
    for (i = 1; i <= DIM; i++) {
        m[x][y] = i;
        if (solveGame(m) == 1)
            return 1;
    }
    m[x][y] = 0;
    return 0;
}

int main(void)
{
    int m[DIM][DIM] = {
        {0,0,1,5,0,0,0,0,0},
        {4,0,0,0,0,0,0,7,0},
        {0,6,0,0,9,0,1,0,0},
        {3,0,0,0,0,1,5,0,0},
        {0,9,0,0,6,0,0,0,8},
        {0,0,5,7,0,0,0,4,0},
        {0,8,0,1,0,0,0,0,2},
        {0,0,3,0,0,0,0,5,0},
        {0,0,0,0,0,2,6,0,0}
    };
    solveGame(m);
    printMatrix(m);
    return 0;
}