YBT高效进阶网络流求最大流

YBT高效进阶网络流求最大流

#include<iostream>
#include<cstdio>
#include<cstring>
#include<queue>
using namespace std;
const long long N=210,E=10010;
long long head[N],to[E],nxt[E],val[E],dep[N],cur[N],t,n,tot=1;
bool vis[N];
void add(long long u,long long v,long long w)
{
    
    
	to[++tot]=v,val[tot]=w,nxt[tot]=head[u],head[u]=tot;
	return;
}
long long BFS(long long s)//分层图，删去无用边
{
    
    
	long long i,u;
	queue<long long>que;
	memset(dep,0,sizeof(dep));
	memset(vis,0,sizeof(vis));
	for(i=1; i<=n; i++)cur[i]=head[i];
	for(dep[s]=1,que.push(s); que.size(); que.pop())
		for(i=head[u=que.front()]; i; i=nxt[i])
			if(val[i]&&!dep[to[i]])
			{
    
    
				dep[to[i]]=dep[u]+1;
				if(!vis[to[i]])
					vis[to[i]]=1,que.push(to[i]);
			}
	return dep[t];
}
long long DFS(long long x,long long flow)
{
    
    
	long long ans=0,sum;
	if(x==t)return flow;
	for(long long &i=cur[x]; i&&ans<flow; i=nxt[i])//当前弧优化:在下一次DFS时不走原来head[x]那条边
		if(val[i]&&dep[x]+1==dep[to[i]]&&(sum=DFS(to[i],min(flow-ans,val[i]))))//上一行:剩余优化:没有剩余流量结束循环
			ans+=sum,val[i]-=sum,val[i^1]+=sum;//多路增广:没有直接返回,继续找增广路
	if(ans<flow)dep[x]=0;//删点优化:有流未增广完,当前点已用极致,下次无需访问该点
	return ans;
}
long long Dinic(long long s)
{
    
    
	long long ans;
	for(ans=0; BFS(s); ans+=DFS(s,0x7f7f7f7f));
	return ans;
}
int main()
{
    
    
	long long m,s,u,v,w,i;
	for(scanf("%lld%lld",&m,&n),s=1,t=n,i=1; i<=m; ++i)
		scanf("%lld%lld%lld",&u,&v,&w),add(u,v,w),add(v,u,0);
	printf("%lld\n",Dinic(s));
	return 0;
}