int solve(int field[][COLS], int row, int col)
{
    int n, m, i;

    if (row*col > 64)       /* solved */
    {
//      output(field);
        return 1;
    }

    n = row;
    m = col;

    n++;            /* set n, m to index of next cell */
    if (n > 8)
    {
    n = 0;
    m++;
    }

    if (field[row][col] == 0)   /* use only empty cells */
    {
        for (i=1; i<=9; i++)    /* search allowed number for the cell */
        {
            if (allowed(field, row, col, i))    /* is i allowed? */
            {
                field[row][col] = i;            /* fill cell with i */
                if (solve(field, n, m))         /* continue with next cell */
        {
                return 1;
        }
                field[row][col] = 0;            /* reset cell if no solution found */
            }
        }
    }

    else    /* if cell is not empty, continue with next cell */
    {
        if (solve(field, n, m))
    {
            return 1;
    }
    }
    return 0;
}