54 lines
1.1 KiB
C++
54 lines
1.1 KiB
C++
#include <algorithm>
|
|
#include <iostream>
|
|
#include <istream>
|
|
#include <queue>
|
|
#include <limits>
|
|
|
|
using std::cin,std::cout;
|
|
|
|
const int MAX_N {(int)2e5+5};
|
|
int n;
|
|
int next[MAX_N];
|
|
int in_degree[MAX_N];
|
|
bool vis[MAX_N];
|
|
std::queue<int> q;
|
|
int ans {std::numeric_limits<int>::max()};
|
|
|
|
int main(){
|
|
std::iostream::sync_with_stdio(false),cin.tie(0),cout.tie(0);
|
|
|
|
std::cin>>n;
|
|
for(int i=1;i<=n;i++){
|
|
cin>>next[i];
|
|
in_degree[next[i]]++;
|
|
}
|
|
const auto push_vis = [](int n){
|
|
q.push(n);
|
|
vis[n]=true;
|
|
};
|
|
for(int i=1;i<=n;i++){
|
|
if(in_degree[i]<=0){
|
|
push_vis(i);
|
|
}
|
|
}
|
|
while(q.empty()==false){
|
|
int front = q.front();
|
|
q.pop();
|
|
if(--in_degree[next[front]]<=0){
|
|
push_vis(next[front]);
|
|
}
|
|
}
|
|
for(int i=1;i<=n;i++){
|
|
if(vis[i])continue;
|
|
int loop_size {0};
|
|
int start {i};
|
|
int now {start};
|
|
do{
|
|
vis[now]=true;
|
|
now=next[now];
|
|
loop_size++;
|
|
}while(now!=start);
|
|
ans=std::min(ans,loop_size);
|
|
}
|
|
std::cout<<ans<<"\n";
|
|
} |