题目链接：
题目：
Network Saboteur
| Time Limit: 2000MS | Memory Limit: 65536K | |
| Total Submissions: 8959 | Accepted: 4190 |
Description
A university network is composed of N computers. System administrators gathered information on the traffic between nodes, and carefully divided the network into two subnetworks in order to minimize traffic between parts.
A disgruntled computer science student Vasya, after being expelled from the university, decided to have his revenge. He hacked into the university network and decided to reassign computers to maximize the traffic between two subnetworks.
Unfortunately, he found that calculating such worst subdivision is one of those problems he, being a student, failed to solve. So he asks you, a more successful CS student, to help him.
The traffic data are given in the form of matrix C, where Cij is the amount of data sent between ith and jth nodes (Cij = Cji, Cii = 0). The goal is to divide the network nodes into the two disjointed subsets A and B so as to maximize the sum ∑Cij (i∈A,j∈B).
A disgruntled computer science student Vasya, after being expelled from the university, decided to have his revenge. He hacked into the university network and decided to reassign computers to maximize the traffic between two subnetworks.
Unfortunately, he found that calculating such worst subdivision is one of those problems he, being a student, failed to solve. So he asks you, a more successful CS student, to help him.
The traffic data are given in the form of matrix C, where Cij is the amount of data sent between ith and jth nodes (Cij = Cji, Cii = 0). The goal is to divide the network nodes into the two disjointed subsets A and B so as to maximize the sum ∑Cij (i∈A,j∈B).
Input
The first line of input contains a number of nodes N (2 <= N <= 20). The following N lines, containing N space-separated integers each, represent the traffic matrix C (0 <= Cij <= 10000).
Output file must contain a single integer -- the maximum traffic between the subnetworks.
Output file must contain a single integer -- the maximum traffic between the subnetworks.
Output
Output must contain a single integer -- the maximum traffic between the subnetworks.
Sample Input
3 0 50 30 50 0 40 30 40 0
Sample Output
90
Source
Northeastern Europe 2002, Far-Eastern Subregion
dfs，枚举的时候确定一部分的电脑数量，然后进行dfs回溯。。。。找出最大值。
只需要搜索一半即可，因为是对称的。。
代码为：
#include<cstdio>
#include<algorithm>
#include<iostream>
using namespace std;
const int maxn=20+10;
int map[maxn][maxn],vis[maxn];
int n,max_value;
void dfs(int s,int num)
{
if(num==0)
{
//cout<<"fuck"<<endl;
int sum=0;
for(int i=1;i<=n;i++)
{
if(!vis[i])
continue;
else
{
for(int j=1;j<=n;j++)
{
if(vis[j])
continue;
else
sum=sum+map[i][j];
}
}
}
// cout<<sum<<endl;
max_value=max(sum,max_value);
return;
}
for(int i=s;i<=n;i++)
{
vis[i]=1;
dfs(i+1,num-1);
vis[i]=0;
}
}
int main()
{
while(scanf("%d",&n)!=EOF)
{
for(int i=1;i<=n;i++)
for(int j=1;j<=n;j++)
scanf("%d",&map[i][j]);
max_value=0;
for(int i=1;i<=n/2;i++)
dfs(1,i);
printf("%d\n",max_value);
}
return 0;
}