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  1.  
  2. #include <bits/stdc++.h>
  3. using namespace std;
  4. #define ll long long
  5. #define endl '\n'
  6. ll N = 1e9+7;
  7. ll oo =1e13;
  8. const ll maxx = 1000000 + 3;
  9. ll n,m,k,q,x,y,z,l,r,mid,ans;
  10. vector<ll>vis;
  11. vector<vector<ll>>adj;
  12.  
  13. void DFS(ll u) {
  14.     vis[u]=1;
  15.     for (ll a:adj[u]) {
  16.         if (vis[a] == 0 ) {
  17.             DFS(a);
  18.         }
  19.     }
  20. }
  21. void solve() {
  22.     cin >> n >> m ;
  23.     vis.assign(n+1,0);
  24.     adj.assign(n+1,{});
  25.     for (ll i =1 ;i <= m;i++) {
  26.         cin>>x>>y;
  27.         adj[y].push_back(x);
  28.         adj[x].push_back(y);
  29.     }
  30.     ll prev=-1;
  31.     vector<pair<ll,ll>>o;
  32.     for (ll i = 1;i<=n;i++) {
  33.         if (!vis[i]) {
  34.             o.push_back({i,prev});
  35.             prev=i;
  36.             DFS(i);
  37.         }
  38.     }
  39.     cout<<o.size()-1<<endl;
  40.     for (ll i =1;i<o.size();i++) {
  41.         cout<<o[i].first<<' '<<o[i].second<<endl;
  42.     }
  43. }
  44. int main() {
  45.     ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0);
  46.     ll t=1 ;
  47.     // cin >>t;
  48.     while (t--) {
  49.         ans=0;
  50.         solve();
  51.     }
  52. }
Success #stdin #stdout 0.01s 5320KB
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https://ideone.com/MLKOQI
language:
C++ (gcc 8.3)
created:
11 hours ago
visibility:
public

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