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  1. #include<bits/stdc++.h>
  2. using namespace std;
  3.  
  4. const long long MaxN = 1e5 + 5;
  5.  
  6. long long n, m;
  7. vector<long long> a[MaxN];
  8. bool visited[MaxN];
  9.  
  10. void input()
  11. {
  12.     cin >> n >> m;
  13.  
  14.     for (long long i = 1; i <= m; i++)
  15.     {
  16.         long long u, v;
  17.         cin >> u >> v;
  18.  
  19.         a[u].push_back(v);
  20.         a[v].push_back(u);
  21.     }
  22. }
  23.  
  24. void dfs(long long s)
  25. {
  26.     stack<long long> st;
  27.  
  28.     st.push(s);
  29.     visited[s] = true;
  30.  
  31.     while (!st.empty())
  32.     {
  33.         long long u = st.top();
  34.         st.pop();
  35.  
  36.         for (long long v : a[u])
  37.         {
  38.             if (!visited[v])
  39.             {
  40.                 visited[v] = true;
  41.                 st.push(v);
  42.             }
  43.         }
  44.     }
  45. }
  46.  
  47. void solve()
  48. {
  49.     if (m != n - 1)
  50.     {
  51.         cout << "NO";
  52.         return;
  53.     }
  54.  
  55.     dfs(1);
  56.  
  57.     for (long long i = 1; i <= n; i++)
  58.     {
  59.         if (!visited[i])
  60.         {
  61.             cout << "NO";
  62.             return;
  63.         }
  64.     }
  65.  
  66.     cout << "YES";
  67. }
  68.  
  69. int main()
  70. {
  71.     input();
  72.     solve();
  73. }
Success #stdin #stdout 0.01s 5980KB
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stdin
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Standard input is empty
stdout
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NO
https://ideone.com/A2Raoa
language:
C++14 (gcc 8.3)
created:
17 hours ago
visibility:
public

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