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  1. #include <bits/stdc++.h>
  2. using namespace std;
  3.  
  4. int main() {
  5.     int n = 8;
  6.     vector<int> targets = {5, 6};
  7.     vector<pair<int, int>> edges = {
  8.         {1, 2}, {2, 5}, {2, 3}, {2, 6}, 
  9.         {1, 4}, {4, 7}, {7, 8}
  10.     };
  11.  
  12.     // build graph
  13.     vector<vector<int>> g(n + 1);
  14.     for (auto [u, v] : edges) {
  15.         g[u].push_back(v);
  16.         g[v].push_back(u);
  17.     }
  18.  
  19.     // bfs from root to get parent pointers
  20.     vector<int> par(n + 1, -1);
  21.     queue<int> q;
  22.     q.push(1);
  23.     par[1] = 0;
  24.  
  25.     while (!q.empty()) {
  26.         int u = q.front();
  27.         q.pop();
  28.         for (int v : g[u]) {
  29.             if (par[v] == -1) {
  30.                 par[v] = u;
  31.                 q.push(v);
  32.             }
  33.         }
  34.     }
  35.  
  36.     // walk up from each target to root, collecting all intermediate nodes
  37.     set<int> nodes;
  38.     nodes.insert(1);
  39.  
  40.     for (int t : targets) {
  41.         nodes.insert(t);
  42.         while (t != 1 && t != 0) {
  43.             t = par[t];
  44.             nodes.insert(t);
  45.         }
  46.     }
  47.  
  48.     // if there's just one node, we don't move
  49.     if (nodes.size() == 1) {
  50.         cout << 0 << endl;
  51.         return 0;
  52.     }
  53.  
  54.     // each edge needs to be traversed twice (down and back up)
  55.     int result = 2 * (nodes.size() - 1);
  56.     cout << result << endl;
  57.  
  58.     return 0;
  59. }
Success #stdin #stdout 0.01s 5316KB
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https://ideone.com/RX0Jeb
language:
C++14 (gcc 8.3)
created:
1 day ago
visibility:
public

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