板子是直接从上一题改过来的，所以一些写法很怪。

不知道是不是写法的原因。

#include <bits/stdc++.h>
#define lc id << 1
#define rc id << 1 | 1
using namespace std;
const int maxn = 2e5 + 10;
int h[maxn * 2], nxt[maxn * 2], to[maxn * 2], w[maxn * 2];
int st[maxn], ed[maxn];
int dfn[maxn], top[maxn], siz[maxn];
int fa[maxn], son[maxn], va[maxn], val[maxn], dep[maxn];
int n, m, cnt, cur;
void add(int u, int v, int val) {
	to[++cnt] = v;
	nxt[cnt] = h[u];
	h[u] = cnt;
	w[cnt] = val;
}
void dfs1(int x, int f){
	fa[x] = f;
	siz[x] = 1;
	dep[x] = dep[f] + 1;
	int sz = -1;
	for(int i = h[x]; i; i = nxt[i]) {
		int v = to[i];
		if(v == f) continue;
		va[v] = w[i];
		dfs1(v, x);
		siz[x] += siz[v];
		if(sz < siz[v])
			sz = siz[v], son[x] = v;
	}
}
void dfs2(int x, int t) {
	top[x] = t;
	dfn[x] = ++cur;
	val[cur] = va[x];
	if(!son[x]) return;
	dfs2(son[x], t);
	for(int i = h[x]; i; i = nxt[i]) {
		int v = to[i];
		if(v == fa[x] || v == son[x])
			continue;
		dfs2(v, v);
	}
}
struct Seg {
	struct node{
		int l, r;
		int sum, laz;
	}a[maxn * 4];
	void maintain(int id) {
		a[id].sum = a[lc].sum + a[rc].sum;
	}
	void maketag(int id) {
		a[id].laz = 1;
		a[id].sum += (a[id].r - a[id].l + 1);
	}
	void pushdown(int id) {
		if(!a[id].laz) return;
		maketag(lc);
		maketag(rc);
		a[id].laz = 0;
	}
	void build(int id, int l, int r) {
		a[id].l = l;
		a[id].r = r;
		if(l == r) {
			a[id].sum = 0;
			return;
		}
		int mid = (l + r) >> 1;
		build(lc, l, mid);
		build(rc, mid + 1, r);
		maintain(id);
	}
	void modify(int id, int l, int r) {
		if(a[id].l >= l && a[id].r <= r) {
			maketag(id);
			return;
		}
		pushdown(id);
		int mid = (a[id].l + a[id].r) >> 1;
		if(l <= mid) modify(lc, l, r);
		if(mid < r) modify(rc, l, r);
		maintain(id);
	}
	int qsum(int id, int l, int r) {
		if(a[id].l >= l && a[id].r <= r)
			return a[id].sum;
		pushdown(id);
		int ret = 0;
		int mid = (a[id].l + a[id].r) >> 1;
		if(l <= mid) ret += qsum(lc, l, r);
		if(mid < r) ret += qsum(rc, l, r);
		return ret;
	}
}T;
int getsum(int x, int y) {
	int ret = 0;
	while(top[x] != top[y]) {
		if(dep[top[x]] < dep[top[y]])
			swap(x, y);
		ret += T.qsum(1, dfn[top[x]], dfn[x]);
		x = fa[top[x]];
	}
	if(dep[x] < dep[y]) swap(x, y);
	ret += T.qsum(1, dfn[y] + 1, dfn[x]);
	return ret;
}
void change(int x, int y) {
	while(top[x] != top[y]) {
		if(dep[top[x]] < dep[top[y]])
			swap(x, y);
		T.modify(1, dfn[top[x]], dfn[x]);
		x = fa[top[x]];
	}
	if(dep[x] < dep[y]) swap(x, y);
	T.modify(1, dfn[y] + 1, dfn[x]);
}
int main() {
	char opt;
	cin >> n >> m;
	for(int i = 1, u, v; i < n; i++) {
		cin >> u >> v;
		add(u, v, 0);
		add(v, u, 0);
	}
	dfs1(1, 0);
	dfs2(1, 1);
	T.build(1, 1, n);
	int u, v;
	while(m--){
		cin >> opt >> u >> v;
		if(opt == 'P') change(u, v);
		if(opt == 'Q') cout << getsum(u, v) << endl;
	}
	return 0;
}