Dinic

#include<iostream>
#include<cstring>
#include<cstdio>
#include<stack>
#define N 1000005
#define inf 0x3f3f3f3f
using namespace std;

struct Edge{
    int to,nxt,cap;
};

int que[N];
int h,qt;

struct Dinic{
    Edge e[N];
    bool vis[N];
    int tot,s,t,n;
    int d[N],cur[N],head[N];
    Dinic(){tot=1;}
    void add(int u,int v,int f){
        e[++tot].to=v;
        e[tot].cap=f;
        e[tot].nxt=head[u];
        head[u]=tot;
        e[++tot].to=u;
        e[tot].cap=0;
        e[tot].nxt=head[v];
        head[v]=tot;
    }
    bool bfs(){
        memset(vis,false,sizeof(vis));
        for(int i=0;i<=n;++i)cur[i]=head[i];
        que[qt=1]=s,h=0;int top,to;d[s]=0;vis[s]=1;
        while(h<qt){
            top=que[++h];
            for(int i=head[top];i;i=e[i].nxt)
                if(!vis[e[i].to]&&e[i].cap){
                    to=e[i].to;que[++qt]=to;
                    vis[to]=true;d[to]=d[top]+1;
                    if(to==t)return true;
                }
        }
        return vis[t];
    }
    int dfs(int x,int fl){
        if(x==t)return fl;
        int flow=0,f,to;
        for(int &i=cur[x];i;i=e[i].nxt){
            to=e[i].to;
            if(d[to]==d[x]+1&&e[i].cap)
            if(f=dfs(to,min(fl,e[i].cap))){
                e[i].cap-=f;fl-=f;
                e[i^1].cap+=f;flow+=f;
                if(fl<=0)break;
            }
        }
        if(fl)d[x]=-1;
        return flow;
    }
    int maxflow(int s,int t){
        this->s=s;this->t=t;
        int ans=0;
        while(bfs())ans+=dfs(s,inf);
        return ans;
    }
};
int main(){
    int n,m,s,t,a,b,c;
    scanf("%d%d%d%d",&n,&m,&s,&t);
    Dinic f;f.n=n;
    for(int i=1;i<=m;++i){
        scanf("%d%d%d",&a,&b,&c);
        f.add(a,b,c);
    }
    cout<<f.maxflow(s,t);
    return 0;
}