HDU - 6214 - Smallest Minimum Cut - 最大流

链接

Dinic模板。

将每条边容量乘上一个大数再加1，跑一次最大流。

然后将最大流模这个大数，能获得最小割的边数。

#include<iostream>
#include<cstring>
#include<string>
#include<vector>
#include<queue>
using namespace std;
typedef long long ll;

const int inf = 0x3f3f3f3f;
const int MAXN = 207;

struct Edge {
    int from, to, cap, flow, w, next;
    Edge(int u = 0, int v = 0, int c = 0, int f = 0): from(u), to(v), cap(c), flow(f) { }
};

struct Dinic {
    int n, m, s, t;
    vector<Edge> edges;
    vector<int> G[MAXN];
    bool vis[MAXN];
    int d[MAXN];
    int cur[MAXN];
    void clear() {
        edges.clear();
        for(int i = 1; i <= MAXN; i++) G[i].clear();
    }

    void add_edge(int u, int v, int cap) {
        edges.push_back(Edge(u, v, cap, 0));
        edges.push_back(Edge(v, u, 0, 0));
        int m = edges.size();
        G[u].push_back(m - 2);
        G[v].push_back(m - 1);
    };

    bool bfs() {
        memset(vis, 0, sizeof(vis));
        queue<int> q;
        q.push(s);
        d[s] = 0;
        vis[s] = 1;
        while(!q.empty()) {
            int x = q.front();
            q.pop();
            for(int i = 0; i < G[x].size(); i++) {
                Edge &e = edges[G[x][i]];
                if(!vis[e.to] && e.cap > e.flow) {
                    vis[e.to] = 1;
                    d[e.to] = d[x] + 1;
                    q.push(e.to);
                }
            }
        }
        return vis[t];
    }
    int dfs(int x, int a) {
        if(x == t || a == 0) return a;
        int flow = 0, f;
        for(int &i = cur[x]; i < G[x].size(); i++) {
            Edge &e = edges[G[x][i]];
            if(d[x] + 1 == d[e.to] && (f = dfs(e.to, min(a, e.cap - e.flow))) > 0) {
                e.flow += f;
                edges[G[x][i] ^ 1].flow -= f;
                flow += f;
                a -= f;
                if(!a) break;
            }
        }
        return flow;
    }
    int maxflow(int s, int t) {
        this->s = s;
        this->t = t;
        int flow = 0;
        while(bfs()) {
            memset(cur, 0, sizeof(cur));
            flow += dfs(s, inf);
        }
        return flow;
    }
};

int main() {
#ifdef LOCAL
    freopen("in.txt", "r", stdin);
#endif
    int t;
    cin >> t;
    while(t--){
        Dinic ans;
        int s ,t,u,v,w,n,m;
        cin >> n >> m;
        cin >> s >> t;
        int mod = 2333;
        for(int i = 0 ;i<m;i++){
            cin >> u >> v >> w;
            ans.add_edge(u,v,w*mod+1);
        }
        int re = ans.maxflow(s, t);
        cout << re%mod << endl;
    }
}