网络流Dinic算法

const int maxn = 1e5+200;
const int  inf = 0x3f3f3f3f;

struct Edge {
    int from, to, cap, flow;
    Edge (int u, int v, int c, int f) : 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 init(int n) {
        for (int i=0; i<n; ++i) G[i].clear();
        edges.clear();
    }
    
    void add(int u, int v , int val) {
        edges.push_back(Edge(u, v, val, 0));
        edges.push_back(Edge(u, v, 0, 0));
        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] = true;
        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] = true;
                    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 == 0) 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;
    }
}Dic;