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;//结点数，边数（包括反向弧），源点编号，汇点编号
    vector<Edge>edges;
    vector<int>g[maxn];
    bool vis[maxn];
    int d[maxn],cur[maxn];
    int p[maxn],num[maxn];

    void init(int n){
        this->n=n;
        for(int i=0;i<=n;++i) g[i].clear();
        edges.clear();
    }

    void add(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);
    }

    bool RevBFS(){
        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();
            for(int i=0;i<g[x].size();i++){
                Edge &e =edges[g[x][i]^1];
                if(!vis[e.from]&&e.cap>e.flow){
                    vis[e.from]=1;
                    d[e.from]=d[x]+1;
                    Q.push(e.from);
                }
            }
        }
        return vis[s];
    }

    int Augment(){
        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;
    }

    int Maxflow(int s,int t){
        this->s=s,this->t=t;
        int flow=0;
        RevBFS();
        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+=Augment();
                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;
    }
};