STOER-WAGNER算法求解无向图最大流最小割(无指定源点汇点)

学习粗：https://blog.csdn.net/ddelphine/article/details/77935670

模板题：http://poj.org/problem?id=2914

#include <iostream>
#include<cstring>
using namespace std;
const int maxn=505;
int mat[maxn][maxn];
int res;
inline int min(int a,int b){if(a<b)return a; return b;}
void Mincut(int n) {
    int node[maxn], dist[maxn];
    bool visit[maxn];
    int i, prev, j, k;
    for (i = 0; i < n; i++)
        node[i] = i;
    while (n > 1) {
        int maxj = 1;
        for (i = 1; i < n; i++) { //初始化到已圈集合的割大小
            dist[node[i]] = mat[node[0]][node[i]];
            if (dist[node[i]] > dist[node[maxj]])
                maxj = i;
        }
        prev = 0;
        memset(visit, false, sizeof (visit));
        visit[node[0]] = true;
        for (i = 1; i < n; i++) {
            if (i == n - 1) { 
            //只剩最后一个没加入集合的点，更新最小割
                res = min(res, dist[node[maxj]]);
                for (k = 0; k < n; k++) 
             //合并最后一个点以及推出它的集合中的点
                    mat[node[k]][node[prev]] = (mat[node[prev]][node[k]] += mat[node[k]][node[maxj]]);
                node[maxj] = node[--n]; //缩点后的图
                continue;
            }
            visit[node[maxj]] = true;
            prev = maxj;
            maxj = -1;
            for (j = 1; j < n; j++)
                if (!visit[node[j]]) { 
                //将上次求的maxj加入集合，合并与它相邻的边到割集
                    dist[node[j]] += mat[node[prev]][node[j]];
                    if (maxj == -1 || dist[node[maxj]] < dist[node[j]])
                        maxj = j;
                }
        }

    }
    return;
}
int main() {
    int n, m, a, b, v;
    while (scanf("%d%d", &n, &m) != EOF) {
        res = (1 << 29);
        memset(mat, 0, sizeof (mat));
        while (m--) {
            scanf("%d%d%d", &a, &b, &v);
            mat[a][b] += v;
            mat[b][a] += v;
        }
        Mincut(n);
        printf("%d\n", res);
    }
    return 0;
}

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