图论：网络流最大流EK算法

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/*
时间复杂度:
O(N*M*M)
*/
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int inf=0x3f3f3f3f;
const int maxn=210;
const int maxm=5e3+10;
int n,m,s,t;
ll maxflow = 0,dis[maxn];

struct edge{
    int v,next;
    ll c;
}e[maxm<<2];
int head[maxn],cnt=0;
int pre[maxn];//pre存上一个点
bool vis[maxn];
int flag[maxn][maxn];

void add(int u,int v,ll c){
    e[cnt].v=v;
    e[cnt].c=c;
    e[cnt].next=head[u];
    head[u]=cnt++;
}

bool bfs(int s,int t){
    for (int i=1;i<=n;i++) vis[i]=0;
    dis[s]=inf;
    vis[s]=1;
    queue<int> q;
    q.push(s);
    while(!q.empty()){
        int u=q.front();
        q.pop();
        for (int i=head[u];~i;i=e[i].next){
            int v=e[i].v;
            ll c=e[i].c;
            // cout<<"c = "<<c<<endl;
            if(c>0 && !vis[v]){
                dis[v]=min(dis[u],c);
                // cout<<"disv = "<<dis[v]<<endl;
                pre[v] = i;
                q.push(v);
                vis[v]=1;
                if(v==t) return 1;//找到了一条增广路
            }
        }
    }
    return 0;
}

void update(int s,int t){
    int x=t;
    while(x!=s){
        int v=pre[x];
        e[v].c-=dis[t];
        e[v^1].c+=dis[t];
        x=e[v^1].v;
    }
    maxflow+=dis[t];
}

void EK(){
    while(bfs(s,t)){
        update(s,t);
    }
}

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-48;ch=getchar();}
	return x*f;
}

ll readll(){
	ll 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-48;ch=getchar();}
	return x*f;
}

int main(){
    cin>>n>>m>>s>>t;
    cnt=0;
    for (int i=1;i<=n;i++) head[i] = -1;
    for (int i=1;i<=m;i++){
        int u,v;
        ll c;
        u=read();v=read();c=readll();
        add(u,v,c);add(v,u,0);
    }
    EK();
    printf("%lld
",maxflow);
    return 0;
}