萌新妹子90pts求调

#include<vector>
#include<iostream>
#define int long long
using namespace std;
const int N=5e5+5;
int n,q,fas[N],dep[N],siz[N],son[N],top[N];
vector<int> edges[N];
void dfs1(int x,int fa){
	fas[x]=fa,siz[x]=1,dep[x]=dep[fa]+1;
	for(int l:edges[x]){
		if(l==fa) continue;
		dfs1(l,x);siz[x]+=siz[l];
		if(siz[l]>siz[son[x]]) son[x]=l;
	}
}
void dfs2(int x,int tot){
	top[x]=tot;
	if(son[x]) dfs2(son[x],tot);
	for(int l:edges[x])
		if(l!=son[x]&&l!=fas[x]) dfs2(l,l);
}
int LCA(int x,int y){
	while(top[x]!=top[y]){
		if(fas[top[x]]<fas[top[y]]) swap(x,y);
		x=fas[top[x]];
	}
	return dep[x]<dep[y]?x:y;
}
signed main(){
	ios::sync_with_stdio(false);
	cin.tie(0);cout.tie(0);
	cin>>n>>q;int f,l,a,b,c,d;
	for(int i=1;i<n;i++){
		cin>>f>>l;
		edges[f].push_back(l);
		edges[l].push_back(f);
	}
	dfs1(1,0);dfs2(1,1);
	while(q--){
		cin>>a>>b>>c>>d;
		int lca1=LCA(a,b),lca2=LCA(c,d);
		if(dep[lca1]>dep[lca2]){
			if(LCA(lca1,c)==lca1||LCA(lca1,d)==lca1) cout<<"Y\n";
			else cout<<"N\n";
		}
		else{
			if(LCA(lca2,a)==lca2||LCA(lca2,b)==lca2) cout<<"Y\n";
			else cout<<"N\n";
		}
	}
	return 0;
}