RT，本地测没问题，交上去全 TLE。

#include<bits/stdc++.h>
#define int long long
using namespace std;
const int N=20500;
struct edge{
	int to,nxt,w;
}e[N*2];
int n,m,s,t,cnt=1,head[N];
int dep[N],flag[N],ans;//dep深度,flag是否在队列中 
int read(){
	int x=0,f=1;
	char ch=getchar();
	while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();}
	while(ch>='0'&&ch<='9'){x=x*10+ch-'0';ch=getchar();}
	return x*f;
}
void add(int u,int v,int w){
	e[++cnt].to=v;
	e[cnt].nxt=head[u];
	e[cnt].w=w;
	head[u]=cnt;
}
bool bfs(){//分层 
	memset(dep,0,sizeof(dep));
	memset(flag,0,sizeof(flag));
	queue<int>q;
	dep[s]=1;
	q.push(s);
	while(!q.empty()){
		int u=q.front();q.pop();
		flag[u]=0;
		for(int i=head[u];i;i=e[i].nxt){
			int v=e[i].to,w=e[i].w;
			if(!dep[v]&&w){
				dep[v]=dep[u]+1;
				if(!flag[v]){
					q.push(v);flag[v]=1;
				}
			}
		}
	}
	if(dep[t])return 1;
	return 0;
}
int dfs(int u,int flow){//找增广路 
	int rlow=0;
	if(u==t)return flow;
	for(int i=head[u];i;i=e[i].nxt){
		int v=e[i].to,w=e[i].w;
		if(w&&dep[v]==dep[u]+1){
			if(rlow=dfs(v,min(flow,w))){
				e[i].w-=rlow;
				e[i^1].w+=rlow;
				return rlow;
			}
		}
	}
}
void Dinic(){
	int lowflow;
	while(bfs()){
		while(lowflow=dfs(s,1145141919810))ans+=lowflow;
	}
}
signed main(){
	n=read();m=read();s=read();t=read();
	for(int i=1;i<=m;i++){
		int u,v,w;u=read();v=read();w=read();
		add(u,v,w);add(v,u,0);//正向边&反向边 
	}
	Dinic();
	printf("%lld",ans);
	return 0;
}