CF 208E. Blood Cousins [dsu on tree 倍增]

题意：给出一个森林，求和一个点有相同k级祖先的点有多少

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倍增求父亲然后和上题一样还不用哈希了...

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <vector>
using namespace std;
typedef long long ll;
#define pii pair<int, int>
#define MP make_pair 
#define fir first
#define sec second
const int N=1e5+5;
int read(){
    char c=getchar();int x=0,f=1;
    while(c<'0'||c>'9'){if(c=='-')f=-1; c=getchar();}
    while(c>='0'&&c<='9'){x=x*10+c-'0'; c=getchar();}
    return x*f;
}

int n, Q, x, k, root[N];
vector<pii> q[N];
int ans[N];
struct edge{int v, ne;}e[N<<1];
int cnt, h[N];
inline void ins(int u, int v) {
	e[++cnt]=(edge){v, h[u]}; h[u]=cnt;
}
int size[N], mx[N], deep[N], big[N], fa[N][18];
void dfs(int u) {
	for(int i=1; (1<<i)<=deep[u]; i++)
		fa[u][i] = fa[fa[u][i-1]][i-1];
	size[u]=1;
	for(int i=h[u];i;i=e[i].ne) {
		deep[e[i].v] = deep[u]+1;
		fa[e[i].v][0] = u;
		dfs(e[i].v);
		size[u] += size[e[i].v];
		if(size[e[i].v] > size[mx[u]]) mx[u] = e[i].v;
	}
}

int f[N];
void update(int u, int val) {
	f[deep[u]]+=val;
	for(int i=h[u];i;i=e[i].ne) if(!big[e[i].v]) update(e[i].v, val);
}
inline int cal(int d) { return d>n ? 0 : f[d] - 1; }
void dfs(int u, int keep) {
	for(int i=h[u];i;i=e[i].ne) 
		if(e[i].v != mx[u]) dfs(e[i].v, 0);
	if(mx[u]) dfs(mx[u], 1), big[mx[u]]=1;
	update(u, 1);
	for(int i=0; i<(int)q[u].size(); i++) ans[q[u][i].fir] = cal(q[u][i].sec);
	big[mx[u]]=0;
	if(!keep) update(u, -1);
}

int main() {
	//freopen("in","r",stdin);
	n=read();
	for(int i=1; i<=n; i++) {
		x=read();
		if(x==0) root[++root[0]]=i;
		else ins(x, i);
	}
	for(int i=1; i<=root[0]; i++) dfs(root[i]);
	Q=read();
	for(int i=1; i<=Q; i++) {
		x=read(); k=read();
		int _=deep[x];
		for(int j=0; j<17; j++) if((1<<j)&k) x=fa[x][j];
		q[x].push_back(MP(i, _));
	}
	for(int i=1; i<=root[0]; i++) dfs(root[i], 0);
	for(int i=1; i<=Q; i++) printf("%d ",ans[i]);
}