공부하느라 만든 Sudoku 계산 프로그램

int matrix[9][9] = {....};
 
int sudoku(int x, int y)
{
    int i,j;
 
    while(matrix[x][y] > 0)
        if (++x >= 9)
        {
            x = 0;
            if (++y >= 9)
                return 0;
        }
 
    do
    {
loop:   if (++matrix[x][y] > 9)
        {
            matrix[x][y]=0;
            return -1;
        }
 
        for (i = 0; i < 9; i++)
            if (i != x && matrix[i][y] == matrix[x][y])
                goto loop;
 
        for (j = 0; j < 9; j++)
            if (j != y && matrix[x][j] == matrix[x][y])
                goto loop;
 
        for (i = (x / 3) * 3; i < (x / 3) * 3 + 3; i++)
            for (j = (y / 3) * 3; j < (y / 3) * 3 + 3; j++)
                if ((i != x || j != y) && matrix[i][j] == matrix[x][y])
                    goto loop;
    } while(sudoku(x, y) == -1);
    return 0;
}
 
int main()
{
    int i, j, r;
 
    r = sudoku(0, 0);
 
    for (i = 0; i < 9; i++)
    {
        for(j = 0; j < 9; j++)
            printf ("\t%d", matrix[i][j]); 
        printf("\n");
    }
 
    return r;
}