网络流最大流ISAP算法（模板）

最大流算法的ISAP算法，Maxflow返回最大流的值

#include<bits/stdc++.h>
using namespace std;
const int inf=2e9;
const int maxn=10050;

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 ISAP{
    int n,m,s,t;
    vector<Edge>edges;
    vector<int>G[maxn];
    bool vis[maxn];
    int d[maxn],cur[maxn];
    int p[maxn],num[maxn];
    void addedge(int from,int to,int cap)
    {
        edges.push_back(Edge(from,to,cap,0));
        edges.push_back(Edge(to,from,0,0));
        int m=edges.size();
        G[from].push_back(m-2);
        G[to].push_back(m-1);
    }

    int Augumemt(){
        int x=t,a=inf;
        while(x!=s){
            Edge&e=edges[p[x]];
            a=min(a,e.cap-e.flow);
            x=edges[p[x]].from;
        }
        x=t;
        while(x!=s){
            edges[p[x]].flow+=a;
            edges[p[x]^1].flow-=a;
            x=edges[p[x]].from;
        }
        return a;
    }

    void bfs(){
        memset(vis,0,sizeof(vis));
        queue<int>q;
        q.push(t);
        d[t]=0;
        vis[t]=1;
        while(!q.empty()){
            int x=q.front();q.pop();
            int len=G[x].size();
            for(int i=0;i<len;i++){
                Edge&e=edges[G[x][i]];
                if(!vis[e.from]&&e.cap>e.flow){
                    vis[e.from]=1;
                    d[e.from]=d[x]+1;
                    q.push(e.from);
                }
            }
        }
    }

    int Maxflow(int s,int t){
        this->s=s;
        this->t=t;
        int flow=0;
        bfs();
        memset(num,0,sizeof(num));
        for(int i=0;i<n;i++) num[d[i]]++;
        int x=s;
        memset(cur,0,sizeof(cur));
        while(d[s]<n){
            if(x==t){
                flow+=Augumemt();
                x=s;
            }
            int ok=0;
            for(int i=cur[x];i<G[x].size();i++){
                Edge&e=edges[G[x][i]];
                if(e.cap>e.flow&&d[x]==d[e.to]+1){
                    ok=1;
                    p[e.to]=G[x][i];
                    cur[x]=i;
                    x=e.to;
                    break;
                }
            }
            if(!ok){
                int m=n-1;
                for(int i=0;i<G[x].size();i++){
                    Edge&e=edges[G[x][i]];
                    if(e.cap>e.flow)
                        m=min(m,d[e.to]);
                }
                if(--num[d[x]]==0)break;
                num[d[x]=m+1]++;
                cur[x]=0;
                if(x!=s) x=edges[p[x]].from;
            }
        }
        return flow;
    }
};