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  1. #include<bits/stdc++.h>
  2. #include<iostream>
  3.  
  4. using namespace std;
  5.  
  6. int n,m;
  7.  
  8. int const N = 200005;
  9.  
  10. vector<int> v[N];
  11.  
  12. vector<bool> visited(N,false);
  13.  
  14. bool cycle = false;
  15.  
  16. void dfs(int i, int parent){
  17.     if(cycle)return;
  18.     visited[i] = true;
  19.  
  20.     for(int node: v[i]){
  21.         if(node==parent)continue;
  22.         if(visited[node]){
  23.             cycle = true;
  24.             return;
  25.         }
  26.         dfs(node,i);
  27.     }
  28. }
  29.  
  30.  
  31. int main()
  32. {
  33.  
  34.     cin >> n >> m;
  35.  
  36.     while(m--){
  37.         int a,b;
  38.  
  39.         cin >> a >> b;
  40.  
  41.         v[a].push_back(b);
  42.         v[b].push_back(a);
  43.     }
  44.  
  45.     for(int i = 1;i<=n;i++){
  46.         if(cycle)break;
  47.         if(!visited[i]){
  48.             dfs(i,-1);
  49.         }
  50.     }
  51.  
  52.     if(!cycle){
  53.         puts("NO");
  54.     }
  55.  
  56.     else{
  57.         puts("YES");
  58.     }
  59.  
  60. }
Success #stdin #stdout 0.01s 8256KB
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stdin
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Standard input is empty
stdout
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NO
https://ideone.com/0pn6Dl
language:
C++14 (gcc 8.3)
created:
10 days ago
visibility:
secret

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