50 lines
1001 B
C++
50 lines
1001 B
C++
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#include <algorithm>
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#include <iostream>
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#include <queue>
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const int MAX_N{int(2e5+5)};
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int in_degree[MAX_N]{},n,next[MAX_N];
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std::queue<int> q;
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bool vis[MAX_N];
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int main(){
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std::cin>>n;
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for(int i=1;i<=n;i++){
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int input;
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std::cin>>input;
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in_degree[input]++;
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next[i]=input;
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}
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for(int i=1;i<=n;i++){
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if(in_degree[i]==0){
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q.push(i);
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}
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}
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while(q.empty()==false){
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int top = q.front();
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in_degree[next[top]]--;
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q.pop();
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if(in_degree[next[top]]==0){
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q.push(next[top]);
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}
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}
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int ans{0};
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for(int i=1;i<=n;i++){
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if(in_degree[i]!=0 && vis[i]==false){
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int begin{i},s{1};
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int now{next[begin]};
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vis[begin]=true;
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while(now!=begin){
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vis[now]=true;
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s++;
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now=next[now];
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}
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ans=std::max(ans,s);
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}
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}
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std::cout<<ans<<"\n";
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}
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