网络流(Edmonds-karp算法 来自汝佳大神)

#include<iostream>
#include<cstdio>

using namespace std;

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 demondskarp{
    int n,m;
    vector<edge>edges;
    vector<int>G[maxn];
    int a[maxn];
    int p[maxn];
    
    void init(int n)
    {
        for(int i=0;i<n;i++){
            G[i].clear();
        }
        edges.clear();
    }
    
    void addedge(int from,int to,int cap)
    {
        edges.push_back(edge(from,to,cap,0));
        edges.push_back(edge(to,from,0,0));
        m=edges.size();
        G[from].push_back(m-2);
        G[to].push_back(m-1);
    }
    
    int maxflow(int s,int t)
    {
        int flow=0;
        for(;;){
            memset(a,0,sizeof(a));
            queue<int>Q;
            Q.push(s);
            a[s]=INF;
            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(!a[e.to]&&e.cap>e.flow){
                        p[e.to]=G[x][i];
                        a[e.to]=min(a[x],e.cap-e.flow);
                        Q.push(e.to);
                    }
                }
                if(a[t]){
                    break;
                }
            }
            if(!a[t]){
                break;
            }
            for(int u=t;u!=s;u=edges[p[u]].from){
                edges[p[u]].flow+=a[t];
                edges[p[u]^1].flow-=a[t];
            }
            flow+=a[t];
        }
        return flow;
    }
};