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