最大流

#include<iostream>
#include<cstring>
#include<queue>
using namespace std;
#define N 50001
#define M 500001
int n,m,x,y,cap;
struct dinic{
    struct graph{
        int tot,head[M];
        struct edge{
            int next;
            int to,dis;
        }ed[M];
        void addEdge(int from,int to,int dis){
            ed[tot].next=head[from];
            ed[tot].to=to,ed[tot].dis=dis;
            head[from]=tot;
            tot++;
        }
        void init(){
            tot=0;
            memset(ed,0,sizeof(ed));
            memset(head,0,sizeof(head));
        }
    }l;
    int deep[N];
    int cur[N];
    int s,t;
    void addEdge(int v,int u,int cap){
        l.addEdge(v,u,cap);
        l.addEdge(u,v,0);
    }
    int dfs(int v,int f){
        if(v==t)return f;
        for(int& i=cur[v];i!=0;i=l.ed[i].next){
            int u=l.ed[i].to,cap=l.ed[i].dis;
            if((deep[u]==deep[v]+1)&&(cap!=0)){
                int di=dfs(u,min(f,cap));
                if(di>0){
                    l.ed[i].dis-=di;
                    l.ed[i^1].dis+=di;
                    return di;
                }
            }
        }
        return 0;
    }
    bool bfs(){
        queue<int>q;
        memset(deep,0,sizeof(deep));
        deep[s]=1;
        q.push(s);
        while(!q.empty()){
            int v=q.front();
            q.pop();
            for(int i=l.head[v];i!=0;i=l.ed[i].next){
                int u=l.ed[i].to,cap=l.ed[i].dis;
                if(deep[u]==0&&cap>0){
                    deep[u]=deep[v]+1;
                    q.push(u);
                }
            }
        }
        return deep[t];
    }
    int execute(){
        int Max=0;
        while(bfs()){
            for(int i=1;i<=n;i++)cur[i]=l.head[i];
            int k=dfs(s,0x7fffffff);
            while(k){
                Max+=k;
                k=dfs(s,0x7fffffff);
            }
        }
        l.init();
        return Max;
    }
}di;
void input(){
    cin>>n>>m>>di.s>>di.t;
    for(int i=1;i<=m;i++){
        cin>>x>>y>>cap;
        di.addEdge(x,y,cap);
    }
}
int main(){
    input();
    cout<<di.execute()<<endl;
}