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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.  
  23. int main(){
  24.     ios::sync_with_stdio(false);
  25.     cin.tie(nullptr);
  26.  
  27.     int T;
  28.     cin >> T;
  29.     while (T--) {
  30.         int n;
  31.         cin >> n;
  32.         // clear adjacency & depths
  33.         for (int i = 1; i <= n; i++) {
  34.             adj[i].clear();
  35.             depths[i].clear();
  36.         }
  37.         maxd = 0;
  38.  
  39.         // read the tree
  40.         for (int i = 2 ; i <= n; i++) {
  41.             int p ; cin >> p ;
  42.             adj[p].push_back(i); 
  43.         }
  44.  
  45.         // bucket nodes by depth starting from node 1
  46.         dfs(1, 0, 0);
  47.  
  48.         // dp[d] = number of ways to choose one node in each depth ≤ d
  49.         vector<ll> dp(maxd+1);
  50.         dp[0] = 1;
  51.         for (int d = 1; d <= maxd; d++) {
  52.             ll cnt = depths[d].size();
  53.             dp[d] = cnt * dp[d-1];
  54.         }
  55.  
  56.         ll res = 0;
  57.         for (int d = 0; d <= maxd; d++) {
  58.             res += dp[d];
  59.         }
  60.         // does thsi realyl wewor kw
  61.         cout << res << "\n";
  62.     }
  63.     return 0;
  64. }
  65.  
Success #stdin #stdout 0.01s 17748KB
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https://ideone.com/SMwt0p
language:
C++ (gcc 8.3)
created:
12 hours ago
visibility:
public

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