Codeforces Round #316 (Div. 2) D. Tree Requests dfs_clock,二分

#include<iostream>
#include<cstring>
#include<cstdio>
#include<ostream>
#include<istream>
#include<algorithm>
#include<queue>
#include<string>
#include<cmath>
#include<set>
#include<map>
#include<stack>
#include<vector>
#define fi first
#define se second
#define pii pair<int,int>
#define inf (1<<30)
#define eps 1e-8
#define ll long long
using namespace std;
const int maxn=510005;
int n,m;
vector<int>g[maxn];
char s[maxn];
vector<int>dep[maxn];
vector<int>op[maxn];
int id[maxn][2];
int deep[maxn];
int mx[maxn];
int dfs_clock=1;
void dfs(int u,int d)
{
    deep[u]=mx[u]=d;
    id[u][0]=dfs_clock++;
    dep[d].push_back(1<<(s[u]-'a'));
    op[d].push_back(id[u][0]);
    for(int i=0;i<g[u].size();i++) {
        dfs(g[u][i],d+1);
        mx[u]=max(mx[u],mx[g[u][i]]);
    }
    id[u][1]=dfs_clock++;
}
int main()
{
    int p;
    scanf("%d%d",&n,&m);
    for(int i=2;i<=n;i++) {
        scanf("%d",&p);
        g[p].push_back(i);
    }
    scanf("%s",s+1);
    dfs(1,1);
    for(int i=1;i<=n;i++) {
        for(int j=1;j<dep[i].size();j++) {
            dep[i][j]^=dep[i][j-1];
        }
    }
    int u,h;
    for(int i=0;i<m;i++) {
        scanf("%d%d",&u,&h);
        if(h<=deep[u] || h>mx[u]) {
            printf("Yes\n");
        }
        else {
            int i=upper_bound(op[h].begin(),op[h].end(),id[u][0])-op[h].begin();
            int j=upper_bound(op[h].begin(),op[h].end(),id[u][1])-op[h].begin()-1;
            int a;
            if(i-1>=0)
                a=dep[h][j]^dep[h][i-1];
            else
                a=dep[h][j];
            int num=0;
            for(int i=0;i<26;i++) {
                if(a&(1<<i))
                    num++;
            }
            if(num<=1)
                printf("Yes\n");
            else
                printf("No\n");
        }
    }
    return 0;
}