sudoku

#include <stdio.h>
#include <stdlib.h>
#define M 9
/*
 *
 */


int get_next_position(int sudoku[M][M], int* f, int* c){
    int i,j;
    for ( i=0;i<M;i++){
        for (j=0;j<M;j++){
            if (sudoku[i][j]==0){
                *f=i;*c=j;
                return 1;
            }
        }
    }
     return 0;
}
void pprint(int sudoku[M][M]){
    int i,j;
    for (i=0;i<M;i++){
        for (j=0;j<M;j++){
            printf("%d ",sudoku[i][j]);
        }
        printf("\n");
    }
}

int numvalido(int sudoku[M][M],int f,int c,int num){
    //filas y columnas
    int i,j;
    for (i=0;i<M;i++){
        if(sudoku[i][c]==num)
            return 0;
        if(sudoku[f][i]==num)
            return 0;
    }

    int i_cuad = (f/3)*3; // OJO: Es división entera porque los operandos son enteros
    int j_cuad = (c/3)*3; // OJO: Es división entera porque los operandos son enteros
    for (i = 0; i < 3; i++)
        for (j = 0; j < 3; j++)
            if (sudoku[i+i_cuad][j+j_cuad] == num)
                return 0;



    //cuadrados
    /*int f_cuad = (f+3)/3;
    int c_cuad = (c+3)/3;
    for (i = 0; i < 3; i++)
        for (j = 0; j < 3; j++)
            if (sudoku[i+(f_cuad-1)*3][j+(c_cuad-1)*3] == num)
                return 0;*/

        return 1;
}


int solve_sudoku(int sudoku[M][M]){
    int f, c,num;
    /* Caso Base: No hay posiciones disponibles*/
    if (!get_next_position(sudoku, &f, &c))
       return 1;

    for(num=1;num<M+1;num++){
        if(numvalido(sudoku,f,c,num)){
            sudoku[f][c]=num;
            if(solve_sudoku(sudoku))
                return 1;
             sudoku[f][c]=0;

        }
    }
    return 0;

}
int main() {

    int sudoku[M][M] = {{3, 0, 6, 5, 0, 8, 4, 0, 0},
                      {5, 2, 0, 0, 0, 0, 0, 0, 0},
                      {0, 8, 7, 0, 0, 0, 0, 3, 1},
                      {0, 0, 3, 0, 1, 0, 0, 8, 0},
                      {9, 0, 0, 8, 6, 3, 0, 0, 5},
                      {0, 5, 0, 0, 9, 0, 6, 0, 0},
                      {1, 3, 0, 0, 0, 0, 2, 5, 0},
                      {0, 0, 0, 0, 0, 0, 0, 7, 4},
                      {0, 0, 5, 2, 0, 6, 3, 0, 0}};
    if (solve_sudoku(sudoku))
          pprint(sudoku);
    else
         printf("No existe solución");

    return 0;
}