poj 2914 Minimum Cut 最小割模板 Stoer-Wagner

连接：http://poj.org/problem?id=2914

Minimum Cut

Time Limit: 10000MS		Memory Limit: 65536K
Total Submissions: 6407		Accepted: 2665
Case Time Limit: 5000MS

Description

Given an undirected graph, in which two vertices can be connected by multiple edges, what is the size of the minimum cut of the graph? i.e. how many edges must be removed at least to disconnect the graph into two subgraphs?

Input

Input contains multiple test cases. Each test case starts with two integers N and M (2 ≤ N ≤ 500, 0 ≤ M ≤ N × (N − 1) ⁄ 2) in one line, where N is the number of vertices. Following are M lines, each line contains M integersA, B and C (0 ≤ A, B < N, A ≠ B, C > 0), meaning that there C edges connecting vertices A and B.

Output

There is only one line for each test case, which contains the size of the minimum cut of the graph. If the graph is disconnected, print 0.

Sample Input

3 3
0 1 1
1 2 1
2 0 1
4 3
0 1 1
1 2 1
2 3 1
8 14
0 1 1
0 2 1
0 3 1
1 2 1
1 3 1
2 3 1
4 5 1
4 6 1
4 7 1
5 6 1
5 7 1
6 7 1
4 0 1
7 3 1

Sample Output

2
1
2

 

#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
const int maxn = 505;
const int INF = 1<<30;
int map[maxn][maxn];
int Sto_wag(int N){
       int dis[maxn],node[maxn],maxj,pre,m,ans=INF;
       bool visit[maxn];
       for(int i = 0; i < N; i ++)node[i] = i;
       while(N > 1){
              m = -1;maxj = 1;
              for(int i = 1; i < N; i ++){
                     dis[node[i]] = map[node[0]][node[i]];
                     visit[node[i]] = 0;
                     if(dis[node[i]] > m){
                            m = dis[node[i]];
                            maxj = i;
                     }
              }
              pre = 0;visit[node[0]] = 1;
              for(int j = 1; j < N; j ++){
                     visit[node[maxj]] = 1;
                     if(j == N-1){
                            ans = min(ans, m);
                            for(int i = 0; i < N; i ++){
                                   map[node[pre]][node[i]] += map[node[maxj]][node[i]];
                                   map[node[i]][node[pre]] += map[node[maxj]][node[i]];
                            }
                            node[maxj] = node[--N];
                     }
                     else{
                            pre = maxj;m = -1;
                            for(int i = 1; i < N; i ++)
                                   if(! visit[node[i]]){
                                          dis[node[i]] += map[node[pre]][node[i]];
                                          if(dis[node[i]] > m){
                                                 m = dis[node[i]];
                                                 maxj = i;
                                          }
                                   }
                     }
              }
       }
       return ans;
}

int main()
{
	int n,m;
	while(~scanf("%d%d",&n,&m)){
	       memset(map,0,sizeof(map));
	       for(int i=0;i<m;i++){
	              int a,b,c;
	              scanf("%d%d%d",&a,&b,&c);
	              map[a][b]+=c;
	              map[b][a]+=c;
	       }
	       printf("%d\n",Sto_wag(n));
	}
	return 0;
}