#include<bits/stdc++.h>
#define lson(root) (root << 1)
#define rson(root) (root << 1 | 1)
using namespace std;
struct node
{
	int to , nxt;
}e[800010];
struct edge
{
	int sum , lazy;
}tree[1600010];
int n , m , tot , head[400010] , dep[400010] , sz[400010] , son[400010] , fa[400010] , tp[400010] , dfn[400010] , cnt = 0 , rk[400010];
void add(int u , int v)
{
	++ tot;
	e[tot].to = v;
	e[tot].nxt = head[u];
	head[u] = tot;
}
void dfs(int u , int pa)
{
	dep[u] = dep[pa] + 1 , sz[u] = 1 , fa[u] = pa;
	for(int i = head[u] ; i != 0 ; i = e[i].nxt)
	{
		int v = e[i].to;
		if(v == pa) continue;
		dfs(v , u);
		sz[u] += sz[v];
		if(sz[son[u]] < sz[v]) son[u] = v;
	}
}
void dfs2(int u , int tp_fa)
{
	dfn[u] = ++ cnt , rk[cnt] = u , tp[u] = tp_fa;
	if(son[u]) dfs2(son[u] , tp_fa);
	for(int i = head[u] ; i != 0 ; i = e[i].nxt)
	{
		int v = e[i].to;
		if(v == fa[u] || v == son[u]) continue;
		dfs2(v , v); 
	}
}
inline void pushup(int root)
{
	tree[root].sum = tree[lson(root)].sum + tree[rson(root)].sum;
}
void pushdown(int root , int l , int r)
{
	if(tree[root].lazy == 0) return;
	int mid = (l + r) >> 1;
	tree[lson(root)].sum += tree[root].lazy * (mid - l + 1);
	tree[rson(root)].sum += tree[root].lazy * (r - mid);
	tree[lson(root)].lazy += tree[root].lazy;
	tree[rson(root)].lazy += tree[root].lazy;
	tree[root].lazy = 0;
}
void update(int root , int l , int r , int L , int R , int val)
{
	if(L <= l && R >= r)
	{
		tree[root].sum += val * (r - l + 1) , tree[root].lazy += val;
		return;
	}
	pushdown(root , l , r);
	int mid = (l + r) >> 1;
	if(L <= mid) update(lson(root) , l , mid , L , R , val);
	if(R > mid) update(rson(root) , mid + 1 , r , L , R , val);
	pushup(root);
}
int query(int root , int l , int r , int pos)
{
	if(l == r) return tree[root].sum;
	int mid = (l + r) >> 1;
	pushdown(root , l , r);
	if(pos <= mid) return query(lson(root) , l , mid , pos);
	else return query(rson(root) , mid + 1 , r , pos);
}
void uv_update(int u , int v)
{
	while(tp[u] != tp[v])
	{
		if(dep[u] < dep[v]) swap(u , v);
		update(1 , 1 , n , dfn[tp[u]] , dfn[u] , 1);
		u = fa[tp[u]];
	}
	if(dep[u] < dep[v]) swap(u , v);
	update(1 , 1 , n , dfn[v] , dfn[u] , 1);
	update(1 , 1 , n , dfn[v] , dfn[v] , -1);
}
int main()
{
	// freopen("P3038_2.in" , "r" , stdin);
	scanf("%d%d" , &n , &m);
	for(int i = 1 ; i < n ; i ++)
	{
		int u , v;
		scanf("%d%d" , &u , &v);
		add(u , v) , add(v , u);
	}
	dfs(1 , 0);
	dfs2(1 , 1);
	while(m --)
	{
		char op;
		int u , v;
		cin >> op , scanf("%d%d" , &u , &v);
		//if(op == 'P') uv_update(u , v);
		//else printf("%d\n" , query(1 , 1 , n , max(dfn[u] , dfn[v])));
	}
	return 0;
}

经过粗略的分段注释，应该是 dfs1 和 dfs2 的问题吧（）