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  1. #include<bits/stdc++.h>
  2. using namespace std;
  3. #define ll long long
  4. #define nmax 200005
  5. vector<int> a[nmax];
  6. ll cha[nmax] , dinhdau = 0 , dinhcuoi = 0;
  7. bool visited[nmax] , instack[nmax] , cycle[nmax];
  8. bool dfs(ll u , ll parent){
  9.     visited[u] = true;
  10.     for (auto i : a[u]){
  11.         if (i == parent){
  12.             continue;
  13.         }
  14.         if (visited[i]){
  15.             dinhdau = i;
  16.             dinhcuoi = u;
  17.             return true;
  18.         }
  19.         else if (!visited[i]){
  20.             cha[i] = u;
  21.             if (dfs(i , u)) return true;
  22.         }
  23.     }
  24.     return false;
  25. }
  26. int main(){
  27.     int n , m;
  28.     cin >> n >> m;
  29.     for (int i = 1 ; i <= m ; i++){
  30.         int x , y;
  31.         cin >> x >> y;
  32.         a[x].push_back(y);
  33.         a[y].push_back(x);
  34.     }
  35.     for (int i = 1 ; i <= n ; i++){
  36.         if (!visited[i]){
  37.             if (dfs(i , -1)){
  38.                 break;
  39.             }
  40.         }
  41.     }
  42.     vector<ll> ans;
  43.     ll cur = dinhcuoi;
  44.     while(cur != dinhdau){
  45.         ans.push_back(cur);
  46.         cur = cha[cur];
  47.     }
  48.     if (dinhdau == 0 or dinhcuoi == 0){
  49.             cout << "IMPOSSIBLE";
  50.             return 0;
  51.     }
  52.     ans.push_back(dinhdau);
  53.     reverse(ans.begin() , ans.end());
  54.     ans.push_back(dinhdau);
  55.     cout << ans.size() << endl;
  56.     for (auto i : ans){
  57.         cout << i << " ";
  58.     }
  59.  
  60.  
  61. //    for (int i = 1 ;i <= n ;i++){
  62. //        cout << cycle[i] << endl;
  63. //    }
  64. }
Success #stdin #stdout 0.01s 9880KB
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IMPOSSIBLE
https://ideone.com/bx5eCp
language:
C++ (gcc 8.3)
created:
2 days ago
visibility:
public

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