POJ 2531 Network Saboteur（dfs）

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題目代號：POJ 2531

題目連結：http://poj.org/problem?id=2531

Language:DefaultNetwork Saboteur

Time Limit: 2000MS		Memory Limit: 65536K
Total Submissions: 13290		Accepted: 6428

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).

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

Output must contain a single integer -- the maximum traffic between the subnetworks.

Sample Input

30 50 3050 0 4030 40 0

Sample Output

90

Source

Northeastern Europe 2002, Far-Eastern Subregion

題目大意：這個題就是題目有點難以理解，相當於有n台伺服器，現在要將n台伺服器分配成2個地區，不同地區之間的任意兩台伺服器會通過兩個地區之間的節點交換資料，現在要你求，節點通過的最大資料量是多少，第i行第j列的數值相當於第i台伺服器與第j台伺服器交換的資料量。

解題思路：dfs遍曆一遍，每遍曆一次擷取最大值，最後輸出就行了。

AC代碼：

# include <stdio.h># include <string.h># include <stdlib.h># include <iostream># include <fstream># include <vector># include <queue># include <stack># include <map># include <math.h># include <algorithm>using namespace std;# define pi acos(-1.0)# define mem(a,b) memset(a,b,sizeof(a))# define FOR(i,a,n) for(int i=a; i<=n; ++i)# define For(i,n,a) for(int i=n; i>=a; --i)# define FO(i,a,n) for(int i=a; i<n; ++i)# define Fo(i,n,a) for(int i=n; i>a ;--i)typedef long long LL;typedef unsigned long long ULL;int a[25][25],ans,n;int b[25];void dfs(int num,int data){    int s=data;    b[num]=1;    for(int i=1;i<=n;i++)    {        if(b[i])data-=a[num][i];        else data+=a[num][i];    }    ans=max(ans,data);    for(int i=num+1;i<=n;i++)    {        if(data>s)        {            dfs(i,data);            b[i]=0;        }    }    return;}int main(){    //freopen("in.txt", "r", stdin);    while(~scanf("%d",&n))    {        for(int i=1;i<=n;i++)            for(int j=1;j<=n;j++)                scanf("%d",&a[i][j]);        ans=0;        mem(b,0);        dfs(1,0);        cout<<ans<<endl;    }    return 0;}

 

POJ 2531 Network Saboteur（dfs）