Codeforces 246E Blood Cousins Return（树上启发式合并）

题目链接 Blood Cousins Return

 #include <bits/stdc++.h>

 using namespace std;

 #define rep(i, a, b) for (int i(a); i <= (b); ++i)

 const int N = ;

 string s[N];
 int ans[N], sz[N], h[N];
 bool skip[N];
 vector <int> v[N];
 vector < pair<int, int> > query[N];
 int n, m, x, y, q;

 unordered_map <string, int> mp[N];

 void getsz(int x){
     sz[x] = ;
     for (auto u : v[x])
         h[u] = h[x] + , getsz(u), sz[x] += sz[u];
 }

 void del(int x){
     auto it = mp[h[x]].find(s[x]);
     --it->second;
     if (!it->second) mp[h[x]].erase(it);
     for (auto u : v[x]) if (!skip[u]) del(u);
 }

 void add(int x){
     mp[h[x]][s[x]]++;
     for (auto u : v[x]) if (!skip[u]) add(u);
 }

 void dfs(int x, bool keep = ){
     int mx = , p = ;
     for (auto u : v[x]) if (mx < sz[u]){ mx = sz[u]; p = u;}
     for (auto u : v[x]) if (u != p) dfs(u, );
     if (p) dfs(p), skip[p] = ;

     add(x);
     for (auto q: query[x])
         ans[q.second] = mp[h[x] + q.first].size();

     if (p) skip[p] = ;
     if (keep) del(x);
 }

 int main(){

     scanf("%d", &n);
     rep(i, , n){
         cin >> s[i] >> x;
         v[x].push_back(i);
     }

     scanf("%d", &q);
     rep(i, , q){
         scanf("%d%d", &x, &y);
         query[x].push_back({y, i});
     }

     getsz();
     dfs();

     rep(i, , q) printf("%d\n", ans[i]);
     return ;
 }