无端RE 0pts 救救MnZn吧

#include <bits/stdc++.h>
using namespace std;

const int N=2e5+10;

int n,m,idx,cnt;
int a[4*N],lan[4*N],val[N];
int head[N],nxt[2*N],ver[2*N];
int id[N],top[N],son[N],fa[N],siz[N],d[N]; 

inline int read(){
	int t=0,f=1;
	register char c=getchar();
	while (c<48||c>57) f=(c=='-')?(-1):(f),c=getchar();
	while (c>=48&&c<=57)t=(t<<1)+(t<<3)+(c^48),c=getchar();
	return f*t;
}

void add(int u,int v){
	nxt[++idx]=head[u];
	head[u]=idx;
	ver[idx]=v;
}

void dfs1(int u,int f){
	int maxx=0;
	d[u]=d[f]+1,siz[u]=1,fa[u]=f;
	for(int i=head[u];i;i=nxt[i]){
		if(ver[i]==f) continue;
		dfs1(ver[i],u);
		siz[u]+=siz[ver[i]];
		if(siz[ver[i]]>maxx) maxx=siz[ver[i]],son[u]=ver[i];
	}
}

void dfs2(int u,int to){
	id[u]=++cnt,top[u]=to;
	if(!son[u]) return;
	dfs2(son[u],to);
	for(int i=head[u];i;i=nxt[i]){
		int dao=ver[i];
		if(dao==fa[u]||dao==son[u]) continue;
		dfs2(dao,dao);
	}
}

void init(){
	dfs1(1,0);
	dfs2(1,1);
}

void pushdown(int bian,int l,int r){
	int mid=(l+r)>>1;
	a[bian<<1]+=(mid-l+1);
	a[bian<<1|1]+=(r-mid);
	lan[bian<<1]+=lan[bian];
	lan[bian<<1|1]+=lan[bian];
	lan[bian]=0;
}

void update(int bian,int l,int r,int L,int R){
	if(L<=l&&R>=r){
		lan[bian]++;
		a[bian]+=r-l+1;
		return; 
	}
	if(lan[bian]) pushdown(bian,l,r);
	int mid=(l+r)>>1;
	if(L<=mid) update(bian<<1,l,mid,L,R);
	if(R>mid) update(bian<<1|1,mid+1,r,L,R);
	a[bian]=a[bian<<1]+a[bian<<1|1];
}

int query(int bian,int l,int r,int C){
	if(l==r) return a[bian];
	if(lan[bian]) pushdown(bian,l,r);
	int mid=(l+r)>>1;
	if(mid<C) query(bian<<1|1,mid+1,r,C);
	else query(bian<<1,l,mid,C);
}

int solve2(int x){return query(1,1,n,id[x]);}

void solve1(int l,int r){
//	bool flag=false;
//	if(l==2&&r==3) flag=true;
	while(top[l]!=top[r]){
		if(d[top[l]]<d[top[r]]) swap(l,r);
		update(1,1,n,id[top[l]],id[l]);
		l=fa[top[l]];
	}
//	if(flag){
//		cout<<"l:"<<l<<" r:"<<r<<endl;
//		for(int i=1;i<=n;i++) cout<<solve2(id[i])<<" ";
//		cout<<endl;
//	}
	if(d[l]>d[r]) swap(l,r);
	if(l!=r) update(1,1,n,id[l]+1,id[r]);
}

void debug(){
	for(int i=1;i<=n;i++) cout<<solve2(id[i])<<" ";
	cout<<endl;
}

int main(){
	n=read(),m=read();
	for(int i=1;i<n;i++){
		int u=read(),v=read();
		add(u,v);add(v,u);
	}
	init();
	while(m--){
		char opt;
		cin>>opt;
		int u=read(),v=read();
		if(d[u]>d[v]) swap(u,v);
		if(opt=='P') solve1(u,v);
		else cout<<solve2(v)<<"\n";
//		debug();
	}
	return 0;
}