Codeforces 570D Tree Requests（树上启发式合并）

题目链接 Tree Requests

#include <bits/stdc++.h>

using namespace std;

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

typedef long long LL;

const int N = 500010;
const int A = 31;

int cntf[N], sz[N], h[N];
vector <int> v[N];
vector <pair<int, int> > query[N];

char s[N];
bool skip[N], cnt[N][A], ans[N];
int n, m, x, y;

void getsz(int x, int dep){
        sz[x] = 1; h[x] = dep;
        for (auto u : v[x]){
            getsz(u, dep + 1);
            sz[x] += sz[u];
        }
}

void add(int x, int val){
    cntf[h[x]] -= cnt[h[x]][s[x] - 'a'];
    cnt[h[x]][s[x] - 'a'] ^= 1;
    cntf[h[x]] += cnt[h[x]][s[x] - 'a'];
        
    for (auto u : v[x]) if (!skip[u]) add(u, val);
}
    

void dfs(int x, bool keep){
        int mx = 0, p;
        for (auto u : v[x]){
                if (sz[u] > mx){
                        mx = sz[u];
                        p = u;
                }
        }
        
        for (auto u : v[x]) if (u != p) dfs(u, 0);
        if (mx) skip[p] = 1, dfs(p, 1);
        
        add(x, 1);
        for (auto q : query[x]){
                ans[q.second] = cntf[q.first] <= 1;
        }
        
        if (mx) skip[p] = 0;
        if (!keep) add(x, -1);
}               

int main(){
    
    scanf("%d%d", &n, &m);
    rep(i, 2, n){
        scanf("%d", &x);
        v[x].push_back(i);
    }
    
    scanf("%s", s + 1);
    
    getsz(1, 1);
    
    rep(i, 1, m){
        scanf("%d%d", &x, &y);
        query[x].push_back({y, i});
    }
    
    memset(ans, 0, sizeof ans);
    dfs(1, 0);
    rep(i, 1, m) puts(ans[i] ? "Yes" : "No");

    return 0;
}