15分，三个点AC了，其它基本全部RE。。。

珂朵莉树+树剖

#include<bits/stdc++.h>
#define ll long long
#define un unsigned
#define pb push_back
#define mp make_pair
using namespace std;
template<typename T> inline void read(T &x){
	x=0;char c=getchar();bool flag=false;
	while(!isdigit(c)){if(c=='-')flag=true;c=getchar();}
	while(isdigit(c)){x=(x<<1)+(x<<3)+(c^48);c=getchar();}
	if(flag)x=-x;
}
template<typename T> inline void write(T x){
   	short st[30],tp=0;
	if(x<0) putchar('-'),x=-x;
	do st[++tp]=x%10,x/=10; while(x);
	while(tp) putchar('0'|st[tp--]);
}
#define wr write
#define rd read
#define pk putchar(' ')
#define ed puts("")
#define it set<node>::iterator
const int maxn=1e5+10;
struct node{
	int l,r;
	mutable ll v;
	node(int L,int R=-1,int V=0):l(L),r(R),v(V) {}
	bool operator < (const node &px)const{
		return l<px.l;
	}
};
set<node>s;
it split(int pos){
	it p=s.lower_bound(node(pos));
	if(p!=s.end()&&p->l==pos) return p;
	--p;
	int L=p->l,R=p->r;
	ll V=p->v;
	s.erase(p);
	s.insert(node(L,pos-1,V));
	return s.insert(node(pos,R,V)).first;
}
void assign(int l,int r,ll V=0){
	it pl=split(l),pr=split(r+1);
	s.erase(pl,pr);
	s.insert(node(l,r,V));
}
struct edge{
	int nxt,to;
}e[2*maxn];
int fa[maxn],deep[maxn],size[maxn],top[maxn],son[maxn],cnt,inde,dfc[maxn],head[maxn],b[maxn],a[maxn];
inline void add(int u,int v){
	e[++cnt].to=v;
	e[cnt].nxt=head[u];
	head[u]=cnt;
}
inline void dfs1(int x,int fat){
	size[x]=1;
	fa[x]=fat;
	son[x]=0;
	size[0]=0;
	for(int i=head[x];i;i=e[i].nxt){
		int y=e[i].to;
		if(y==fat) continue;
		deep[y]=deep[x]+1;
		dfs1(y,x);
		size[x]+=size[y];
		if(size[y]>size[son[x]]) son[x]=y;
	}
}
inline void dfs2(int x,int fat,int t){
	dfc[x]=++inde;
	a[inde]=b[x];
	top[x]=t;
	if(!son[x]) return;
	dfs2(son[x],x,t);
	for(int i=head[x];i;i=e[i].nxt){
		int y=e[i].to;
		if(y==fat||y==son[x]) continue;
		dfs2(y,x,y);
	}
}
inline void edge_assign(int x,int y,int v){
	while(top[x]!=top[y]){
		if(deep[top[x]]<deep[top[y]]) swap(x,y);
		assign(dfc[top[x]],dfc[x],v);
		x=fa[top[x]];
	}
	if(deep[x]>deep[y]) swap(x,y);
	assign(dfc[x],dfc[y],v);
}
inline int edge_query(int x,int y){
	int ans=0,last1=0,last2=0;
	it itl,itr;
	while(top[x]!=top[y]){
		if(deep[top[x]]>deep[top[y]]){
			itr=split(dfc[x]+1),itl=split(dfc[top[x]]);
			for(--itr;;--itr){
				if(itr->v!=last1) last1=itr->v,++ans;
				if(itr==itl) break;
			}
			x=fa[top[x]];
		}
		else{
			itr=split(dfc[y]+1),itl=split(dfc[top[y]]);
			for(--itr;;--itr){
				if(itr->v!=last2) last2=itr->v,++ans;
				if(itr==itl) break;
			}
			y=fa[top[y]];
		}
	}
	if(deep[x]>deep[y]){
			itr=split(dfc[x]+1),itl=split(dfc[y]);
			for(--itr;;--itr){
				if(itr->v!=last1) last1=itr->v,++ans;
				if(itr==itl) break;
			}
			x=fa[top[x]];
		}
		else{
			itr=split(dfc[y]+1),itl=split(dfc[x]);
			for(--itr;;--itr){
				if(itr->v!=last2) last2=itr->v,++ans;
				if(itr==itl) break;
			}
			y=fa[top[y]];
		}
	return ans-(last1==last2);
}
signed main(){
	int q,n,i,x,y,v;
	rd(n),rd(q);
	char opt;
	for(i=1;i<=n;i++) rd(b[i]);
	for(i=1;i<n;i++){
		rd(x),rd(y);
		add(x,y);
		add(y,x);
	}
	dfs1(1,0);
	dfs2(1,0,1);
	for(i=1;i<=n;i++) s.insert(node(i,i,a[i]));
	//for(i=1;i<=n;i++) wr(a[i]),pk;
	//ed;
	while(q--){
		cin>>opt>>x>>y;
		if(opt=='C'){
			cin>>v;
			edge_assign(x,y,v);
		}
		else{
			wr(edge_query(x,y)),ed;
		}
	}
}

求调