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  1. #include <iostream>
  2. #include <vector>
  3. #include <queue>
  4. #include <algorithm>
  5.  
  6. using namespace std;
  7.  
  8. void convertToDirectedTree(vector<vector<int>>& adj, int root, vector<vector<int>>& directedAdj) {
  9.     int n = adj.size();
  10.     vector<bool> visited(n, false);
  11.     queue<int> q;
  12.  
  13.     q.push(root);
  14.     visited[root] = true;
  15.  
  16.     while (!q.empty()) {
  17.         int node = q.front();
  18.         q.pop();
  19.  
  20.         for (int neighbor : adj[node]) {
  21.             if (!visited[neighbor]) {
  22.                 directedAdj[node].push_back(neighbor);
  23.                 visited[neighbor] = true;
  24.                 q.push(neighbor);
  25.             }
  26.         }
  27.     }
  28. }
  29.  
  30. int main() {
  31.     int n, root;
  32.     cin >> n;
  33.     vector<vector<int>> adj(n), directedAdj(n);
  34.     for (int i = 0; i < n - 1; i++) {
  35.         int u, v;
  36.         cin >> u >> v;
  37.         adj[u].push_back(v);
  38.         adj[v].push_back(u);
  39.     }
  40.  
  41.     cin >> root;
  42.  
  43.     convertToDirectedTree(adj, root, directedAdj);
  44.     vector<pair<int, int>> edges;
  45.     for (int i = 0; i < n; i++) {
  46.         for (int v : directedAdj[i]) {
  47.             edges.emplace_back(i, v);
  48.         }
  49.     }
  50.  
  51.     sort(edges.begin(), edges.end());
  52.  
  53.     for (const auto& edge : edges) {
  54.         cout << edge.first << " " << edge.second << endl;
  55.     }
  56.  
  57.     return 0;
  58. }
Success #stdin #stdout 0.01s 5288KB
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stdin
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5
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2 4
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4 1
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stdout
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1 0
4 1
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4 3
https://ideone.com/eycYwp
language:
C++14 (gcc 8.3)
created:
6 days ago
visibility:
public

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