fork download
copy 
  1. #include <bits/stdc++.h>
  2.  
  3. const int N = 200005;
  4. using namespace std;
  5.  
  6. vector<pair<int, int>> edges;
  7. vector<int> adj[N];
  8. int low[N], num[N], cnt[N], parent[N], sz[N];
  9. bool isBridge[N];
  10. int n, m, timer, cntBridge, cc;
  11.  
  12. void dfs(int u) {
  13.   num[u] = ++timer;
  14.   low[u] = num[u];
  15.   cnt[cc]++;
  16.   sz[u] = 1;
  17.  
  18.   for (int v : adj[u]) {
  19.     if (v == parent[u])
  20.       continue;
  21.  
  22.     if (num[v]) {
  23.       low[u] = min(low[u], num[v]);
  24.     } else {
  25.       parent[v] = u;
  26.       dfs(v);
  27.       low[u] = min(low[u], low[v]);
  28.       sz[u] += sz[v];
  29.  
  30.       if (low[v] > num[u]) {
  31.         cntBridge++;
  32.         isBridge[v] = true;
  33.       }
  34.     }
  35.   }
  36. }
  37.  
  38. long long solve() {
  39.   if (cc > 2)
  40.     return 0;
  41.   if (cc == 2)
  42.     return (long long)cnt[1] * cnt[2] * (m - cntBridge);
  43.  
  44.   long long ans = 0;
  45.   long long maxE = (long long)n * (n - 1) / 2;
  46.  
  47.   for (const auto &edge : edges) {
  48.     int u = edge.first;
  49.     int v = edge.second;
  50.     if (num[u] > num[v])
  51.       swap(u, v);
  52.     if (parent[v] == u && isBridge[v]) {
  53.       ans += (long long)sz[v] * (sz[1] - sz[v]) - 1;
  54.     } else {
  55.       ans += maxE - m;
  56.     }
  57.   }
  58.   return ans;
  59. }
  60.  
  61. int main() {
  62.   ios::sync_with_stdio(0);
  63.   cin.tie(0);
  64.  
  65.   cin >> n >> m;
  66.   for (int i = 0; i < m; i++) {
  67.     int u, v;
  68.     cin >> u >> v;
  69.     adj[u].push_back(v);
  70.     adj[v].push_back(u);
  71.     edges.push_back({u, v});
  72.   }
  73.  
  74.   for (int i = 1; i <= n; i++) {
  75.     if (num[i] == 0) {
  76.       cc++;
  77.       dfs(i);
  78.     }
  79.   }
  80.  
  81.   cout << solve();
  82.   return 0;
  83. }
  84.  
Success #stdin #stdout 0.01s 9624KB
comments (?)
stdin
copy 
Standard input is empty
stdout
copy 
Standard output is empty
https://ideone.com/FDmoha
language:
C++14 (gcc 8.3)
created:
6 days ago
visibility:
public

Share or Embed source code

Discover > Sphere Engine API

The brand new service which powers Ideone!

Discover > IDE Widget

Widget for compiling and running the source code in a web browser!