67 lines
1.3 KiB
C++
67 lines
1.3 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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#include <vector>
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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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std::vector<int> next[MAX_N];
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int in_degree[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 input;
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int dfs(const int start, const int now, int depth){
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depth++;
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vis[now] = true;
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int max_depth{ depth };
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for (int i : next[now]) {
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if (i == start) {
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max_depth = std::max(max_depth, depth);
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}
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else {
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max_depth = std::max(dfs(start, i, depth), max_depth);
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}
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}
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return max_depth;
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};
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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>>input;
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in_degree[input]++;
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next[i].push_back(input);
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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(in_degree[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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for(int i:next[front]){
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if(--in_degree[i]<=0){
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push_vis(i);
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}
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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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ans=std::max(ans,dfs(i,i,0));
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}
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cout<<ans<<"\n";
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} |