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  1. #include <bits/stdc++.h>
  2. using namespace std;
  3. #define nl '\n'
  4. #define ll long long 
  5.  
  6. void fastio() {
  7.     ios_base::sync_with_stdio(false);
  8.     cin.tie(nullptr);
  9.     cout.tie(nullptr);
  10. }
  11. vector<bool>visited;
  12. vector<vector<int>>adj;
  13.  
  14. bool cyclic = false;
  15. void dfs(int node,int p){
  16.     visited[node]=true;
  17.  
  18.     for(auto child : adj[node]){
  19.         if(child == p)
  20.             continue;
  21.  
  22.         if(!visited[child]){
  23.             dfs(child,node);
  24.         }
  25.         else{
  26.             cyclic =true;
  27.         }
  28.     }
  29. }
  30. void solve() {
  31.     int n,e;cin >> n>> e;
  32.     int u,v;
  33.     adj.assign(n+1,{});
  34.     visited.assign(n+1,false);
  35.     for(int i=0;i<e;i++){
  36.         cin >> u >> v;
  37.         adj[u].push_back(v);
  38.         adj[v].push_back(u);
  39.     }
  40.  
  41.  
  42.     for(int i=1;i<=n;i++){
  43.         if(!visited[i]){
  44.             dfs(i,i);
  45.         }
  46.  
  47.     }
  48.     if(cyclic) cout <<"There is a cycle\n";
  49.     else cout <<"There is not a cycle\n";
  50.  
  51. }
  52.  
  53. int main() {
  54.     fastio();
  55.     int t=1;
  56.     //cin >> t;
  57.     while (t--) 
  58.         solve();
  59.     return 0;
  60. }
  61.  
Success #stdin #stdout 0.01s 5288KB
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stdout
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There is a cycle
https://ideone.com/Er3kV9
language:
C++ (gcc 8.3)
created:
1 day ago
visibility:
public

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