最大流模板

P3376 【模板】网络最大流

#include<bits/stdc++.h>
#define fo(i,a,b) for (ll (i)=(a);(i)<=(b);(i)++)
#define fd(i,b,a) for (ll (i)=(b);(i)>=(a);(i)--)
#define lc (o<<1)
#define rc ((o<<1)|1)
#define mk(x,y) make_pair((x),(y))
#define eb emplace_back
#define A puts("Yes")
#define B puts("No")
#define fi first
#define se second
using namespace std;
typedef double db;
typedef long long ll;
typedef unsigned long long ull;
typedef long long i64;
const ll inf=1ll<<60;
const ll mo1=1e9+9;
const ll mo2=1e9+7;
const ll P=131;
const ll Q=13331;
struct MF {
	const static int N=1e5+5;
	const static int M=1e6+5;
	const static int INF=1e9;
  	struct edge {
    	int v, nxt;
		ll cap, flow;
  	} e[M*2];

  	int head[N], tot = 0;

  	int n, S, T;
  	ll maxflow = 0;
  	int dep[N], cur[N];
  	MF(int nn,int s,int t)	{
  		n=nn;
  		S=s;
  		T=t;
  		memset(head, -1, sizeof head);
    	tot = 0;
 	}
  	void init() {
  		
    	memset(head, -1, sizeof head);
    	tot = 0;
  	}

	void addedge(int u, int v, int w) {
    	e[tot] = {v, head[u], w, 0};
    	head[u] = tot++;
    	e[tot] = {u, head[v], 0, 0};
    	head[v] = tot++;
  	}	

  	bool bfs() {
    	queue<int> q;
    	memset(dep, 0, sizeof(int) * (n + 1));

   		dep[S] = 1;
	    q.push(S);
	    while (q.size()) {
	    	int u = q.front();
	      	q.pop();
	      	for (int i = head[u]; ~i; i = e[i].nxt) {
	       		int v = e[i].v;
	        	if ((!dep[v]) && (e[i].cap > e[i].flow)) {
	          		dep[v] = dep[u] + 1;
	          		q.push(v); 
	        	}
	      	}
	    }
	    return dep[T];
	}

	ll dfs(int u, ll flow) {
		if ((u == T) || (!flow)) return flow;
	
		ll ret = 0;
	    for (int& i = cur[u]; ~i; i = e[i].nxt) {
			int v = e[i].v;
			ll d;
		    if ((dep[v] == dep[u] + 1) &&
		        (d = dfs(v, min(flow - ret, e[i].cap - e[i].flow)))) {
		        ret += d;
		        e[i].flow += d;
		        e[i ^ 1].flow -= d;
		        if (ret == flow) return ret;
		    }
	    }
	    return ret;
	}

  	void dinic() {
  		maxflow = 0;
    	while (bfs()) {
      		memcpy(cur, head, sizeof(int) * (n + 1));
      		maxflow += dfs(S, INF);
    	}
  	}
};
int n,m,s,t,x,y,z;
int main(){
//	freopen("data.in","r",stdin);

	scanf("%d %d %d %d",&n,&m,&s,&t);
	MF mf(n,s,t);
	
	fo(i,1,m) {
		scanf("%d %d %d",&x,&y,&z);
		mf.addedge(x,y,z);
	}
	
	mf.dinic();
	printf("%lld\n",mf.maxflow);
	

	return 0;
}