POJ 2531 Network Saboteur

　　枚举了所有状态 1800+ms过了......

　　

#include <iostream>
#include <algorithm>
#include <cstdio>
#include <cstdlib>
#include <cstring>

using namespace std;

int c[25][25];

int MaxSum;

bool MarkSubSet[25];

void dfs(int cur,int ans,int Sum,int n)
{
    if(cur > n)
    {
        int i,j,sum;
        for(i = 1,sum = 0; i <= n; ++i)
        {
            if(MarkSubSet[i])
            {
                for(j = 1; j <= n; ++j)
                {
                    if(MarkSubSet[j] == false)
                        sum += c[i][j];
                }
            }
        }
        MaxSum = MaxSum > sum ? MaxSum : sum ;
        return ;
    }
    MarkSubSet[cur] = true;
    dfs(cur+1,ans+1,Sum,n);
    MarkSubSet[cur] = false;
    dfs(cur+1,ans,Sum,n);
}

int main()
{

    int n,i,j;
    while(scanf("%d",&n) != EOF)
    {

        for(i = 1; i <= n; ++i)
        {
            for(j = 1; j <= n; ++j)
                scanf("%d",&c[i][j]);
        }

        MaxSum = -1;
        memset(MarkSubSet,false,sizeof(MarkSubSet));

        dfs(1,0,n/2,n);

        printf("%d
",MaxSum);
    }
    return 0;
}