[模板][最大流]dinic

 最大流 = 最小割

#pragma GCC optimize(2)
#include <bits/stdc++.h>
#define m(x) memset(x, 0, sizeof(x))
using namespace std;
typedef long long ll;

const int MAXN = 1e6 + 10;
 
ll inf = ll(1) << 29;

struct MF
{
	const static int maxn = 1e6 + 10;
	ll n, m, s, t, maxflow;
	ll head[maxn], ver[maxn << 1], edge[maxn << 1], Next[maxn << 1], d[maxn], tot;
	
	void init()
	{
		tot = 1;
		memset(head, 0, sizeof(head));
	}
	
	void add(ll x, ll y, ll z)
	{
		ver[++tot] = y, edge[tot] = z, Next[tot] = head[x], head[x] = tot;
		ver[++tot] = x, edge[tot] = 0, Next[tot] = head[y], head[y] = tot;
	}
	
	bool bfs() 
	{
		memset(d, 0, sizeof(d));
		queue <int> q;
		q.push(s); d[s] = 1;
		while(!q.empty())
		{
			int x = q.front(); q.pop();
			for(int i = head[x]; i; i = Next[i])
			{
				if(edge[i] && !d[ver[i]])
				{
					q.push(ver[i]);
					d[ver[i]] = d[x] + 1;
					if(ver[i] == t)
						return true;
				}
			}
		}
		return false;
	}
	
	ll dinic(ll x, ll flow)
	{
		if(x == t) return flow;
		ll rest = flow, k;
		for(ll i = head[x]; i && rest; i = Next[i])
		{
			if(edge[i] && d[ver[i]] == d[x] + 1)
			{
				k = dinic(ver[i], min(rest, edge[i]));
				if(!k) d[ver[i]] = 0;
				edge[i] -= k;
				edge[i ^ 1] += k;
				rest -= k;
			}
		}
		return flow - rest;
	}
	
	ll cal()
	{
		ll flow = 0, maxflow = 0;
		while(bfs())
			while(flow = dinic(s, inf)) maxflow += flow;
		return maxflow;
	}
};
 
int main()
{

    ios::sync_with_stdio(false);

    cin.tie(0);     cout.tie(0);
    
    MF M;
    M.init();
    
	cin >> M.n >> M.m >> M.s >> M.t;
	
    ll a, b, c;
	
    for(int i = 0; i < M.m; ++i)
    {
    	cin >> a >> b >> c;
    	M.add(a, b, c);
	}
	
	cout << M.cal() << '
';		

    return 0;
}