P3376 【模板】网络最大流

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P3376 【模板】网络最大流

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Code

#include<bits/stdc++.h>
using namespace std;
typedef long long LL;
const int maxn=205,maxe=10005,INF=1<<30;
int N,M,S,T,lnk[maxn],nxt[maxe],son[maxe],w[maxe],cnt=1,Min_x[maxn],pre[maxn],vis[maxn],Q[maxn];
LL Ans;
inline void add_e(int x,int y,int z){
	son[++cnt]=y;w[cnt]=z;nxt[cnt]=lnk[x];lnk[x]=cnt;
}
inline int read(){
	int ret=0,f=1;char ch=getchar();
	while(ch<'0'||ch>'9'){if(ch=='-')f=-f;ch=getchar();}
	while(ch<='9'&&ch>='0')ret=ret*10+ch-'0',ch=getchar();
	return ret*f;
}
bool bfs(){
	memset(vis,0,sizeof vis);
	int hed=0,til=1;Q[til]=S;vis[S]=1;
	Min_x[S]=INF;
	while(hed!=til){
		hed++;
		for(int j=lnk[Q[hed]];j;j=nxt[j]){
			if(w[j]){
				if(vis[son[j]])continue;
				Min_x[son[j]]=min(Min_x[Q[hed]],w[j]);
				pre[son[j]]=j;
				Q[++til]=son[j];vis[son[j]]=1;
				if(son[j]==T)return 1;
			}
		}
	}
	return 0;
}

void update(){
	int x=T;
	while(x!=S){
		int i=pre[x];
		w[i]-=Min_x[T];
		w[i^1]+=Min_x[T];
		x=son[i^1];
	}
	Ans+=(LL)Min_x[T];
}
int main(){
	freopen("P3376.in","r",stdin);
	freopen("P3376.out","w",stdout);
	N=read();M=read();S=read(),T=read();
	for(int i=1;i<=M;i++){
		int x=read(),y=read(),z=read();
		add_e(x,y,z);
		add_e(y,x,0);
	}
	while(bfs())
		update();
	printf("%lld
",Ans);
	return 0;
}