rt。

经过几轮调试，样例已过。

但一个点都跑不过去。

#include<cstdio>
#include<algorithm>
#define maxn 1000010
#define Inf 0x3f3f3f3f
using namespace std;
inline int read(){
	register int d=0,f=1;char ch = getchar();
	while(ch<'0'||ch>'9'){
		if(ch=='-')
			f=-1;
		ch=getchar();
	}
	while(ch>='0'&&ch<='9'){
		d = (d<<1)+(d<<3)+(ch^48);
		ch = getchar();
	}
	return d*f;
}
void writes(int x){
	if(x>9) writes(x/10);
	putchar(x%10+48);
}
inline void write(int x){
	if(x<0) putchar('-'),writes(-x);
	else writes(x);
	putchar('\n');
}
int edgeCnt;
struct Edge{
	int to,nxt;
}edge[maxn];
int head[maxn];
int fa[maxn];
int siz[maxn];
int w[maxn],wt[maxn];
int son[maxn];
int id[maxn];
int top[maxn];
int dep[maxn];
int col[maxn];
int ncol[maxn];
int n,m,r,cnt;
struct Node{
	int lc,rc,val,tag;
}tree[maxn<<4];
void add(int u,int v){
	edge[++edgeCnt].to=v;
	edge[edgeCnt].nxt=head[u];
	head[u]=edgeCnt;
}
void pushdown(int x){
	if(tree[x].tag){
		tree[x<<1].lc=tree[x].tag;
		tree[x<<1].rc=tree[x].tag;
		tree[x<<1].tag=tree[x].tag;
		tree[x<<1].val=1;
		tree[x<<1|1].lc=tree[x].tag;
		tree[x<<1|1].rc=tree[x].tag;
		tree[x<<1|1].tag=tree[x].tag;
		tree[x<<1|1].val=1;
		tree[x].tag=0;
	}
}
void build(int rt,int l,int r){
	if(l==r){
		tree[rt].lc=tree[rt].rc=ncol[l];
		tree[rt].val=1;
		tree[rt].tag=0;
		return ;
	}
	int mid=(l+r)>>1;
	build(rt<<1,l,mid);
	build(rt<<1|1,mid+1,r);
	tree[rt].lc=tree[rt<<1].lc,tree[rt].rc=tree[rt<<1|1].rc;
	tree[rt].val=tree[rt<<1].val+tree[rt<<1|1].val-(tree[rt<<1].rc==tree[rt<<1|1].lc);
}
void update(int rt,int l,int r,int ql,int qr,int col){
	if(ql<=l&&r<=qr){
		tree[rt].val=1;
		tree[rt].lc=col;
		tree[rt].rc=col;
		tree[rt].tag=col;
		return ;
	}
	int mid=(l+r)>>1;
	pushdown(rt);
	if(ql<=mid) update(rt<<1,l,mid,ql,qr,col);
	if(mid<qr) update(rt<<1|1,mid+1,r,ql,qr,col);
	tree[rt].lc=tree[rt<<1].lc,tree[rt].rc=tree[rt<<1|1].rc;
	tree[rt].val=tree[rt<<1].val+tree[rt<<1|1].val-(tree[rt<<1].rc==tree[rt<<1|1].lc);
}
int L,R;
int query(int rt,int l,int r,int ql,int qr){
	if(ql==l) L=tree[rt].lc;
	if(qr==r) R=tree[rt].rc;
	if(ql<=l&&r<=qr){
		return tree[rt].val;
	}
	int mid=(l+r)>>1,ans=0;
	pushdown(rt);
	if(ql<=mid) ans+=query(rt<<1,l,mid,ql,qr);
	if(mid<qr) ans+=query(rt<<1|1,mid+1,r,ql,qr);
	return ans;
}
void Update(int x,int y,int col){
	while(top[x]!=top[y]){
		if(dep[top[x]]<dep[top[y]]) swap(x,y);
		update(1,1,n,id[top[x]],id[x],col);
		x=fa[top[x]];
	}
	if(dep[x]>dep[y]) swap(x,y);
	update(1,1,n,id[x],id[y],col);
}
int Query(int x,int y){
	int res=0,ans1=0,ans2=0;
	while(top[x]!=top[y]){
		if(dep[top[x]]<dep[top[y]]) swap(x,y),swap(ans1,ans2);
		res+=query(1,1,n,id[top[x]],id[x]);
		if(R==ans1) res--;
		x=fa[top[x]];
		ans1=L;
	}
	if(dep[x]>dep[y]) swap(x,y),swap(ans1,ans2);
	res+=query(1,1,n,id[x],id[y]);
	if(ans1==R) res--;
	if(ans2==L) res--;
	return res;
}
void dfs1(int x,int Fa,int deep){
	dep[x]=deep;
	siz[x]=1;
	fa[x]=Fa;
	int maxx=-Inf;
	for(int i=head[x];i;i=edge[i].nxt){
		int y=edge[i].to;
		if(y==Fa) continue;
		dfs1(y,x,deep+1);
		siz[x]+=siz[y];
		if(siz[y]>maxx) maxx=siz[y],son[x]=y;
	}
}
void dfs2(int x,int tops){
	top[x]=tops;
	id[x]=++cnt;
	ncol[id[x]]=col[x];
	if(!son[x]) return ;
	dfs2(son[x],tops);
	for(int i=head[x];i;i=edge[i].nxt){
		int y=edge[i].to;
		if(y==fa[x]||y==son[x]) continue;
		dfs2(y,y);
	}
}
char op[maxn];
signed main(){
	n=read(),m=read();
	for(int i=1;i<=n;i++) col[i]=read();
	for(int i=1;i<n;i++){
		int u=read(),v=read();
		add(u,v);add(v,u);
	}
	dfs1(1,0,1);
	dfs2(1,1);
	build(1,1,n);
	while(m--){
		scanf("%s",op);
		if(op[0]=='C'){
 			int a=read(),b=read(),c=read();
			Update(a,b,c);
		}
		else{
			int a=read(),b=read();
			write(Query(a,b));
		}
	} 
	return 0;
}
/*
        1
       / \
      2   3 
     /|\
    4 5 6
*/