POJ 2531

#include <stdio.h>
#include <iostream>
#define MAXN  21
using namespace std;

int _m[MAXN][MAXN];
int flag[MAXN];

int n;
int index;
int _max;
int num;
void DFS(int time);
int main()
{
    //freopen("acm.acm","r",stdin);
    //freopen("out.acm","w",stdout);
    int i;
    int j;
    memset(flag,0,sizeof(flag));
    cin>>n;
    _max = -1;
    index = 1;
    for(i = 0; i < n; ++ i)
    {
        for(j = 0; j < n; ++ j)
        {
            scanf("%d",&_m[i][j]);
        }
    }
    for(index = 1; index <= n/2+1; ++ index)
    {
        num = 0;
        DFS(0);
    }
    cout<<_max<<endl;
    return 0;
}

void DFS(int time)
{
    if(time == n)
        return;
    if(num == index)
    {
        int i;
        int j;
        int sum = 0;
        for(i = 0; i < n; ++ i)
        {
            for(j = i+1;j < n; ++ j)
            {
                if(flag[i] != flag[j])
                {
                    sum += _m[i][j];
                }
            }
        }
        if(sum > _max)
        {
            _max = sum;
        }
        return;
    }
    flag[time] = 1;
    ++ num;
    DFS(time + 1);
    -- num;
    flag[time] = 0;
    DFS(time + 1);
}