又来主席树第一发：dfs序-代代宗师

#include<iostream>
#include<vector>
#include<string.h>
#define N 105000
#define L 2*N
using namespace std;
vector<int>vec[N];
int v[2*N],vl,st[N],ed[N];
int sur[N],hgt[N],mxhgt;
bool vis[N];
void dfs(int x,int h)
{
	vis[x]=true;
	v[++vl]=x;st[x]=vl;hgt[vl]=h;
	if (h>mxhgt)mxhgt=h;
	for (int i=0;i<vec[x].size();i++)
		if (!vis[vec[x][i]])dfs(vec[x][i],h+1);
	v[++vl]=x;ed[x]=vl;hgt[vl]=-1;
}
struct PD_tree
{
	struct node
	{
		int sum;
		int l,r;
		node *lc,*rc;
		node(){sum=0;l=r=0;}
		node(int h1,int h2,int h3){l=h1,r=h2;sum=h3;}
	};
	node *root[L];
	void build(int l,int r,node* &pnt)
	{
		pnt=new node(l,r,0);
		if (l<r){
			int mid=(l+r)>>1;
			build(l,mid,pnt->lc);build(mid+1,r,pnt->rc);
		} else pnt->lc=pnt->rc=NULL;
	}
	void update(node* last,node* &now,int x)
	{
		now=new node(last->l,last->r,last->sum);
		if (now->l==now->r){
			if ((now->l)==x)(now->sum)++;
			//if (x==6)cerr<<"YES\n";
			return;
		}
		int mid=((last->l)+(last->r))>>1;
		if (x>mid){now->lc=last->lc;update(last->rc,now->rc,x);}
			else {now->rc=last->rc;update(last->lc,now->lc,x);}
		now->sum=(now->lc->sum)+(now->rc->sum);
		//cerr<<last->l<<" "<<last->r<<" "<<x<<"\n";
	}
	int find(node* now,int x)
	{
		if (now->l==now->r)return now->sum;
		
		int mid=(now->l+now->r)>>1;
		if (x<=mid)return find(now->lc,x);
			else return find(now->rc,x);
	}
void display(node* now)
{
	if (now->l==now->r){cout<<now->sum<<" ";return;}
	display(now->lc);display(now->rc);
}
}t;
int main()
{
	ios::sync_with_stdio(false);
	int n,q,i;
	cin>>n>>q;
	for (i=1;i<=n;i++)cin>>sur[i];
	for (i=1;i<n;i++){
		int v1,v2;
		cin>>v1>>v2;
		vec[v1].push_back(v2);vec[v2].push_back(v1);
	}
	vl=0;mxhgt=0;
	memset(vis,false,sizeof(vis));
	dfs(1,1);
	t.build(1,mxhgt,t.root[0]);
	for (i=1;i<=vl;i++){
		if (sur[v[i]]&&hgt[i]!=-1)t.update(t.root[i-1],t.root[i],hgt[i]);
			else t.root[i]=t.root[i-1];
		//cerr<<"OOPS:"<<v[i]<<" "<<t.find(t.root[i],hgt[i])<<"\n";
	}
	/*for (i=1;i<=vl;i++)
	{cerr<<v[i]<<" ";t.display(t.root[i]);cerr<<"\n";}*/
	
	for (i=1;i<=q;i++){
		int vi,hi;
		cin>>vi>>hi;
		//cerr<<"U:"<<ed[vi]<<" "<<st[vi]<<"\n";
		cout<<(t.find(t.root[ed[vi]],hi)-t.find(t.root[st[vi]-1],hi))<<"\n";//打少-1扣了一次
	}
	return 0;
}