Uva 167 The Sultan's Successors(dfs)

题目链接：Uva 167

思路分析：八皇后问题，采用回溯法解决问题。

代码如下：

#include <iostream>
#include <string.h>
using namespace std;

const int MAX_N = ;
int A[MAX_N];
int M[MAX_N][MAX_N];
int num, Max = ;

int is_safe( int row, int col )
{
    for ( int i = ; i < row; ++i )
    {
        if ( A[i] == col )
            return false;
        if ( A[i] + i == row + col )
            return false;
        if ( i - A[i] == row - col )
            return false;
    }

    return true;
}

void dfs( int row )
{
    if ( row ==  )
    {
        for ( int i = ; i < ; ++i )
            num += M[i][A[i]];
        if ( num > Max )
            Max = num;

        num = ;
        return;
    }
    else
    {
        for ( int i = ; i < ; ++i )
        {
            if ( is_safe( row , i ) )
            {
                A[row] = i;
                dfs( row+ );
            }

        }
    }
}

int main( )
{
    int n;

    cin >> n;
    while ( n-- )
    {
        num = Max = ;
        memset( M, , sizeof( M ) );
        memset( A, , sizeof( A ) );

        for ( int i = ; i <= ; ++i )
            for ( int j = ; j <= ; ++j )
                cin >> M[i][j];

        dfs(  );
        printf( "%5d\n", Max );
    }

    return ;
}