68 lines
1.4 KiB
C++
68 lines
1.4 KiB
C++
#include <algorithm>
|
|
#include <iostream>
|
|
#include <istream>
|
|
#include <queue>
|
|
#include <vector>
|
|
#include <functional>
|
|
|
|
using std::cin,std::cout;
|
|
|
|
const int MAX_N {(int)2e5+5};
|
|
int n;
|
|
std::vector<int> next[MAX_N];
|
|
int in_degree[MAX_N];
|
|
bool vis[MAX_N];
|
|
std::queue<int> q;
|
|
int ans;
|
|
int input;
|
|
|
|
int dfs(const int start, const int now, int depth){
|
|
depth++;
|
|
vis[now] = true;
|
|
int max_depth{ depth };
|
|
for (int i : next[now]) {
|
|
if (i == start) {
|
|
max_depth = std::max(max_depth, depth);
|
|
}
|
|
else {
|
|
max_depth = std::max(dfs(start, i, depth), max_depth);
|
|
}
|
|
}
|
|
return max_depth;
|
|
};
|
|
|
|
int main(){
|
|
std::iostream::sync_with_stdio(false),cin.tie(nullptr),cout.tie(nullptr);
|
|
|
|
std::cin>>n;
|
|
for(int i=1;i<=n;i++){
|
|
cin>>input;
|
|
in_degree[input]++;
|
|
next[i].push_back(input);
|
|
}
|
|
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();
|
|
for(int i:next[front]){
|
|
if(--in_degree[i]<=0){
|
|
push_vis(i);
|
|
}
|
|
}
|
|
|
|
}
|
|
|
|
for(int i=1;i<=n;i++){
|
|
if(vis[i])continue;
|
|
ans=std::max(ans,dfs(i,i,0));
|
|
}
|
|
cout<<ans<<"\n";
|
|
} |