RT，求大佬们抽出少许时间帮助我这只蒟蒻/kel

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
const int N=500010;
const ll inf=2005020000;
int n,m,s,t,u,v,book[3000][3000],pre[N],head[N],cnt=1;
bool vis[N];
ll w,ans,dis[N];
queue <int> q; 
struct edge{
    int to,nex;
    ll val;
}e[N];
inline void add(int a,int b,ll c){
    e[++cnt].to=b;
    e[cnt].val=w;
    e[cnt].nex=head[a];
    head[a]=cnt;
}
inline bool bfs(){
    memset(vis,0,sizeof(vis));
    while(q.size()) q.pop();
    q.push(s);vis[s]=1;
    dis[s]=inf;
    while(!q.empty()){
        int x=q.front();q.pop();
        for(int i=head[x];i;i=e[i].nex){
            if(!e[i].val) continue;
            int to=e[i].to;
            if(vis[to]) continue;
            dis[to]=min(dis[x],e[i].val);pre[to]=i;
            vis[to]=1;q.push(to);
            if(to==t) return 1;
        }
    }
    return 0;
}
inline void update(){
    int a=t;
    while(a!=s){
        int b=pre[a];
        e[b].val-=dis[t];
        e[b^1].val+=dis[t];
        a=e[b^1].to;
    }
    ans+=dis[t];
}
int main(){
    scanf("%d%d%d%d",&n,&m,&s,&t);
    while(m--){
        cin>>u>>v>>w;
        if(!book[u][v]) add(u,v,w),add(v,u,0),book[u][v]=cnt;
        else e[book[u][v]-1].val+=w;
    }
    while(1)
        if(bfs()) update();
        else break;
    printf("%lld\n",ans);
    return 0;
}

record:https://www.luogu.com.cn/record/36378093