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  1. #include <bits/stdc++.h>
  2. #define FNAME "circuit"
  3. using namespace std;
  4. typedef long long ll;
  5. const int MAXN = (int)2e5 + 1;
  6. #define xd '\n'
  7. #define pii pair<int, int>
  8. #define pil pair<int, long long>
  9. const long long MOD = 1e9 + 15092007;
  10.  
  11. void fastip() {
  12.     ios_base::sync_with_stdio(0);
  13.     cin.tie(0); cout.tie(0);
  14.     if (fopen(FNAME".inp", "r")) {
  15.         freopen(FNAME".inp", "r", stdin);
  16.         freopen(FNAME".out", "w", stdout);
  17.     }
  18. }
  19.  
  20. struct Edge{
  21.     int u, v;
  22.     bool eID;
  23. };
  24.  
  25. int n, s;
  26. vector<Edge> edge;
  27. vector<vector<int>> adj;
  28. vector<int> Ans;
  29. vector<int> List;
  30.  
  31. void Euler(int s){
  32.     stack<int> st;
  33.     st.push(s);
  34.  
  35.     while(!st.empty()){
  36.         int u = st.top();
  37.         bool check = false;
  38.  
  39.         for(int id : adj[u]){
  40.             bool cID = edge[id].eID;
  41.             if(!cID){
  42.                 edge[id].eID = true;
  43.                 check = true;
  44.                 st.push((edge[id].u == u) ? edge[id].v : edge[id].u);
  45.                 break;   
  46.             }
  47.         }
  48.  
  49.         if(!check) {
  50.             Ans.push_back(u);
  51.             st.pop();
  52.         }
  53.     }
  54. }
  55.  
  56. signed main(){
  57.     fastip();
  58.  
  59.     cin >> n >> s;
  60.  
  61.     adj.resize(n + 1);
  62.  
  63.     int u, v;
  64.  
  65.     while(cin >> u >> v) {
  66.         edge.push_back({u, v, false});
  67.         int id = edge.size() - 1;
  68.         adj[u].push_back(id);
  69.         adj[v].push_back(id);
  70.     }
  71.  
  72.     Euler(s);
  73.     reverse(Ans.begin(), Ans.end());
  74.  
  75.     for(int i = 0; i < Ans.size() ; i++){
  76.         if(Ans[i] == s && i != 0){
  77.             cout << "YES";
  78.             return 0;
  79.         }
  80.     }
  81.  
  82.     cout << "NO";
  83.  
  84.     return 0;
  85. }
  86.  
Success #stdin #stdout 0.01s 5320KB
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stdin
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Standard input is empty
stdout
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NO
https://ideone.com/R6i5g8
language:
C++ (gcc 8.3)
created:
6 hours ago
visibility:
public

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