洛谷 P3376【模板】网络最大流（网络流模板）

传送门

#include
using namespace std;
#define ll long long

const int maxn = 100005;
const int maxm = 2000005;
const int inf = 0x3f3f3f3f;

struct DINIC
{
	struct node
	{
		int u,v,w,next;
	}edge[maxm];
	int deep[maxn],dl[maxm],fir[maxm];
	int cnt,aim;
	void init()
	{
		memset(fir,-1,sizeof fir);
		cnt=0;
	}
	void add(int u,int v,int w)
	{
		edge[cnt].u=u,edge[cnt].v=v,edge[cnt].w=w;
        edge[cnt].next=fir[u];fir[u]=cnt++;
        edge[cnt].u=v,edge[cnt].v=u,edge[cnt].w=0;
        edge[cnt].next=fir[v];fir[v]=cnt++;
	}
	bool bfs(int S,int T)
	{
		memset(deep, 0, sizeof deep);
		deep[S] = 1;dl[1] = S;
		int head = 0, tail = 1;
		while(head != tail){
			int v = dl[++head];
			for(int u = fir[v]; ~u; u = edge[u].next){
				if(edge[u].w && !deep[edge[u].v]){
					deep[edge[u].v] = deep[v]+1;
					dl[++tail] = edge[u].v;
				}
			}
		}
		return deep[T];
	} 
	int dfs(int now, int fl)
	{
		if(now == aim) return fl;
		int f = 0;
		for(int u = fir[now]; ~u && fl; u = edge[u].next){
			if(edge[u].w && deep[edge[u].v] == deep[now]+1){
				int x = dfs(edge[u].v, min(fl,edge[u].w));
				edge[u].w -= x;
				edge[u^1].w += x;
				fl -= x;
				f += x;
			}
		}
		if(!f) deep[now] = -2;
		return f;
	}
	int maxflow(int S,int T)
	{
		aim = T; 
		int ans = 0;
		while(bfs(S, T)) ans += dfs(S, inf);
		return ans;
	}
}dinic;

int main()
{
	//n个点，m条边，求S到T的最大流/最小割（dinic算法） 
	int n,m;
	while(~scanf("%d%d",&n,&m)){
		int S,T;
		scanf("%d%d",&S,&T);
		dinic.init();
		
		for(int i=1;i<=m;i++){
			int u,v,w;
			scanf("%d%d%d",&u,&v,&w);
			dinic.add(u,v,w);
		}
		printf("%d\n",dinic.maxflow(S,T));
	}
	return 0;
}