RT，交了八遍。拍了几千组小数据没错，又拍了几组极限数据也没错，求好心的巨佬帮忙找找虫子QAQ。不胜感激awa

#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cstring>
#include<cmath>
#include<vector>
#define ll long long
#define fo(i,x,y) for(register int i=x;i<=y;++i)
#define go(i,x,y) for(register int i=x;i>=y;--i)
using namespace std;
inline int read(){int x=0,fh=1; char ch=getchar(); while(!isdigit(ch)){if(ch=='-') fh=-1; ch=getchar();} while(isdigit(ch)){x=(x<<1)+(x<<3)+ch-'0'; ch=getchar();} return x*fh;}

const int N=1e6+5;
struct Edge{
	int to,next;
}e[N];
int head[N],tot,_tmp[N],st[N],ed[N],dfn,fa[N][20],dep[N],lg,blk,L=1,R,Ans,cnt[N],P[N],n,m;
int tmp[N],col[N],ans[N],od[N],bel[N];

void connect(int x,int y){
	e[++tot]=(Edge){y,head[x]};
	head[x]=tot;
} 

struct Ask{
	int u,v,l,r,num,fl;
	void init(){
		u=read(),v=read();
		if(st[u]>st[v]) swap(u,v);
		if(st[u]<=st[v]&&ed[v]<=ed[u]) fl=0,l=st[u],r=st[v];
		else fl=1,l=ed[u],r=st[v];
	}
	bool operator<(const Ask &x)const{return bel[l]!=bel[x.l]?(bel[l]<bel[x.l]):(r<x.r);}
}a[N];

void dfs(int x,int fr){
	dep[x]=dep[fr]+1;
	fa[x][0]=fr;
	st[x]=++dfn;col[dfn]=tmp[x];
	for(int i=head[x];i;i=e[i].next){
		int p=e[i].to;
		if(p==fr) continue;
		dfs(p,x);
	}
	ed[x]=++dfn;col[dfn]=tmp[x];
	P[st[x]]=ed[x];
	P[ed[x]]=st[x];
}

inline int lca(int x,int y){
	if(dep[x]>dep[y]) swap(x,y);
	go(i,lg,0) if(dep[fa[y][i]]>=dep[x]) y=fa[y][i];
	if(x==y) return x;
	go(i,lg,0) if(fa[x][i]!=fa[y][i]) x=fa[x][i],y=fa[y][i];
	return fa[x][0];
}

void del(int x){if(--cnt[x]==0) Ans--;}
void add(int x){if(cnt[x]++==0) Ans++;}

bool cmp(int x,int y){return _tmp[x]<_tmp[y];} 

int main(){
	cin>>n>>m;lg=log(n)/log(2);blk=sqrt(2*n);
	fo(i,1,n) _tmp[i]=read(),od[i]=i;
	sort(od+1,od+1+n,cmp);
	int rp=0;
	fo(i,1,n){
		if(_tmp[od[i]]>_tmp[od[i-1]]) rp++;
		tmp[od[i]]=rp;
	}//fo(i,1,n) printf("%d ",tmp[i]);puts("");
	fo(i,1,n<<1) bel[i]=(i-1)/blk;
	fo(i,1,n-1){
		int x=read(),y=read();
		connect(x,y);
		connect(y,x);
	}
	dfs(1,0);
	fo(i,1,n)
		fo(j,1,lg) fa[i][j]=fa[fa[i][j-1]][j-1];
	fo(i,1,m) a[i].init(),a[i].num=i;
	sort(a+1,a+1+m);
	fo(i,1,m){
		while(L<a[i].l){
			if(P[L]<L||P[L]>R) del(col[L]);
			else add(col[L]);
			++L;
		}
		while(L>a[i].l){
			--L;
			if(P[L]<L||P[L]>R) add(col[L]);
			else del(col[L]);
		}
		while(R<a[i].r){
			++R;
			if(P[R]<L||P[R]>R) add(col[R]);
			else del(col[R]);
		}
		while(R>a[i].r){
			if(P[R]<L||P[R]>R) del(col[R]);
			else add(col[R]);
			R--;
		}
		if(a[i].fl){
			int k=lca(a[i].u,a[i].v);
			add(tmp[k]);
			ans[a[i].num]=Ans;
			del(tmp[k]);
		}else ans[a[i].num]=Ans;
	}
	fo(i,1,m) printf("%d\n",ans[i]);
	return 0;
}