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  1. #include<bits/stdc++.h>
  2. using namespace std;
  3. #define ll long long
  4. vector<int> a[100005];
  5. ll dp[100005];
  6. ll dfs(ll u){
  7.     if (dp[u] != - 1){
  8.         return dp[u];
  9.     }
  10.     ll ans = 0;
  11.     for (auto i : a[u]){
  12.         ans = max(ans , dfs(i) + 1);
  13.     }
  14.     return dp[u] = ans;
  15. }
  16. void solve(){
  17.     ll n , m;
  18.     cin >> n >> m;
  19.     for (int i = 1 ; i <= m ; i++){
  20.         ll x ,y;
  21.         cin >> x >> y;
  22.         a[x].push_back(y);
  23.     }
  24.     memset(dp , -1 , sizeof(dp));
  25.     ll ans = 0;
  26.     for (ll i = 1 ; i <= n ; i++){
  27.         ans = max(ans , dfs(i));
  28.     }
  29.     cout << ans;
  30. }
  31. int main(){
  32.     solve();
  33. }
  34.  
Success #stdin #stdout 0.01s 6656KB
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https://ideone.com/6hDZUp
language:
C++ (gcc 8.3)
created:
8 days ago
visibility:
public

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