并查集裸题，记录每个点的胜读，取个min就好了

#include
     
      #include
      
       #include
       
        using namespace std;int fa[200007],dep[200007],n,x,a,mn=1e9+7;template
        
         void read(T &x){	int f=0;x=0;char ch=getchar();	while(ch<'0'||ch>'9')  {f|=(ch=='-');ch=getchar();}	while(ch>='0'&&ch<='9'){x=(x<<1)+(x<<3)+(ch^48);ch=getchar();}	x=f?-x:x;}int find(int x){	if(fa[x]!=x) {int t=fa[x];fa[x]=find(fa[x]);dep[x]+=dep[t];}	return fa[x];}void yhh(int a,int b){	int x=find(a),y=find(b);	if(x!=y) fa[x]=y,dep[a]=dep[b]+1;	else     mn=min(mn,dep[a]+dep[b]+1);}int main(){	read(n);	for(int i=1;i<=n;++i)	  fa[i]=i;	for(int i=1;i<=n;++i)	  read(x),yhh(i,x);	printf("%d",mn);	return 0;}