算法要素:并查集的奇妙应用

思路：

并查集求有向图最小环

tips：这道题完全可以拓展成带边权的有向图最小环，原题相当于边权为1.

Code

#include<bits/stdc++.h>
using namespace std;
const int maxn=2e5+50;
int fa[maxn],dis[maxn];
int n,t[maxn];
int minn=1e9+7;
int Find(int x)
{
	if(fa[x]!=x)
	{
		int last=fa[x];
		fa[x]=Find(fa[x]);
		dis[x]+=dis[last];	
	}
	return fa[x];
}	
void check(int x,int y)
{
	int xx=Find(x),yy=Find(y);
	if(xx!=yy)
	{
		dis[x]=dis[y]+1;
		fa[xx]=yy;
	}
	else minn=min(minn,dis[y]+dis[x]+1);
	return;
}
int main()
{
	scanf("%d",&n);
	for(int i=1;i<=n;++i) scanf("%d",&t[i]);
	for(int i=1;i<=n;++i) fa[i]=i;
	for(int i=1;i<=n;++i)
	{
		check(i,t[i]);
	}
	printf("%d",minn);
	return 0;	
}

标签：NOIP2015,有向图,洛谷,int,fa,maxn,Find,dis
来源： https://www.cnblogs.com/mint-hexagram/p/15546452.html