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POJ 1149 PIGS

#include <iostream>
#include<queue> 
#include <cstring>
#define IOS std::ios::sync_with_stdio(0)
using namespace std;
 const int N =1000,M=5e5+100;
#define int long long 
 
 const int inf =1e9;
 int R[N],a[N];
 int all=1,hd[N],go[M],w[M],nxt[M];
  
 int S,T,n,m;
 int dis[M],ans=0,now[M];
  
 void add_(int x,int y,int z){
    nxt[++all]=hd[x]; hd[x]=all; go[all]=y;
    w[all]=z;
    swap(x,y);
    nxt[++all]=hd[x]; hd[x]=all; go[all]=y;
    w[all]=0;
 }
  bool bfs(){
    for(int i=1;i<=n+m+3;i++)dis[i]=inf;
    queue<int> q;
    q.push(S);
    now[S]=hd[S];
    dis[S]=0;
     
    while(q.empty()==0){
        int x=q.front(); 
        q.pop();
        for(int i=hd[x];i;i=nxt[i]){
            int y=go[i];
            if(w[i]>0&&dis[y]==inf){
                dis[y]=dis[x]+1;
                now[y]=hd[y];
                q.push(y);
                if(y==T) return 1;
            }
        }
    }
    return 0;
 }
 int dfs(int x,int sum){
    if(x==T) return sum;
    int k,res=0;
     
    for(int i=now[x];i&∑i=nxt[i]){
        now[x]=i;
        int y=go[i]; 
        if(w[i]>0&&(dis[y]==dis[x]+1)){
            k=dfs(y,min(sum,w[i]));
            if(k==0) dis[y]=inf;
            w[i]-=k;
            w[i^1]+=k;
            res+=k;
            sum-=k;
        }
    }
    return res;
 }
  
 signed main(){
    IOS;
    int i,x,y,z;
    cin>>n>>m>>S>>T;
    for(i=1;i<=m;i++){
        cin>>x>>y>>z; add_(x,y,z); 
    }
    int ans=0;
    while(bfs()) ans+=dfs(S,inf);
    cout<<ans<<endl;
 }