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  1. #include <bits/stdc++.h>
  2. using namespace std;
  3.  
  4. using ll = long long;
  5. const int MAXN = 300000;
  6.  
  7. vector<int> adj[MAXN+1];
  8. vector<int> depths[MAXN+1];
  9. int maxd;
  10.  
  11. void dfs(int u, int p, int d) {
  12.     // record node u at depth d
  13.     depths[d].push_back(u);
  14.     maxd = max(maxd, d);
  15.     // recurse on children
  16.     for (int v : adj[u]) {
  17.         if (v == p) continue;
  18.         dfs(v, u, d+1);
  19.     }
  20. }
  21.  
  22. int main(){
  23.     ios::sync_with_stdio(false);
  24.     cin.tie(nullptr);
  25.  
  26.     int T;
  27.     cin >> T;
  28.     while (T--) {
  29.         int n;
  30.         cin >> n;
  31.         // clear adjacency & depths
  32.         for (int i = 1; i <= n; i++) {
  33.             adj[i].clear();
  34.             depths[i].clear();
  35.         }
  36.         maxd = 0;
  37.  
  38.         // read the tree
  39.         for (int i = 0; i < n-1; i++) {
  40.             int a, b;
  41.             cin >> a >> b;
  42.             adj[a].push_back(b);
  43.             adj[b].push_back(a);
  44.         }
  45.  
  46.         // bucket nodes by depth starting from node 1
  47.         dfs(1, 0, 0);
  48.  
  49.         // dp[d] = number of ways to choose one node in each depth ≤ d
  50.         vector<ll> dp(maxd+1);
  51.         dp[0] = 1;
  52.         for (int d = 1; d <= maxd; d++) {
  53.             ll cnt = depths[d].size();
  54.             dp[d] = cnt * dp[d-1];
  55.         }
  56.  
  57.         // sum up dp[0] + dp[1] + ... + dp[maxd]
  58.         ll res = 0;
  59.         for (int d = 0; d <= maxd; d++) {
  60.             res += dp[d];
  61.         }
  62.  
  63.         cout << res << "\n";
  64.     }
  65.     return 0;
  66. }
  67.  
Success #stdin #stdout 0.01s 17656KB
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https://ideone.com/DeI0DV
language:
C++ (gcc 8.3)
created:
12 hours ago
visibility:
public

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