dinic板子

loj上偷学长的（

注意几点：

id初值赋1才能让正向弧反向弧对应起来

很多题要拆点，一定保证空间

dfs里rest=0的终止条件不能放在for循环里

#include<cstdio>
#include<iostream>
#include<bits/stdc++.h>
#define ll long long
using namespace std;
inline int read(int x=0,char ch=getchar()){
    while(!isdigit(ch)) ch=getchar();
    while(isdigit(ch)) x=(x<<3)+(x<<1)+(ch^48),ch=getchar();
    return x;
}

const int N=1e2+7,M=1e4+7;
const ll inf=1e18;

int n,m,S,T;
ll ans,c[M];
int head[N],to[M],nx[M],id=1;
inline void add(int a,int b,int cc){
    nx[++id]=head[a]; head[a]=id; to[id]=b; c[id]=cc;
}
inline void Add(int a,int b,int c){
    add(a,b,c); add(b,a,0);
}

int q[N],hd,tl;
int dis[N],Hd[N];

inline bool bfs(){
    memset(dis,0x3f,sizeof(dis));
    memcpy(head,Hd,sizeof(head));
    q[hd=tl=1]=S; dis[S]=0;
    while(hd<=tl){
        int x=q[hd++];
        for(int i=head[x];i;i=nx[i]) if(c[i]){
            int t=to[i];
            if(dis[t]>dis[x]+1){
                dis[t]=dis[x]+1;
                q[++tl]=t;
            }
        }
        if(x==T) return 1;
    }
    return 0;
}

ll dfs(int x,ll in){
    if(x==T) return in;
    ll rest=in,go;
    for(int i=head[x];i;head[x]=i=nx[i]) if(c[i]){
        int t=to[i];
        if(dis[t]==dis[x]+1){
            go=dfs(t,min(rest,c[i]));
            if(go) c[i]-=go,c[i^1]+=go,rest-=go;
            else dis[t]=0;
        }
        if(!rest) break;
    }
    return in-rest;
}

int main(){
    n=read(); m=read();
    S=read(); T=read();
    while(m--){
        int u=read(),v=read();
        Add(u,v,read());
    }
    memcpy(Hd,head,sizeof(Hd));
    while(bfs()) ans+=dfs(S,inf);
    printf("%lld\n",ans);
    return 0;
}