莫名RE，甚至我还不能保证我代码有没有其他跟输出答案正确与否的错误 code：

#include<cstdio>
#include<iostream>
#include<string>
#include<cstring>
using namespace std;

const int MAXN = 4e6 + 17;
const int INF = 1e9 + 17;

struct node
{
	int v,next;
}e[MAXN];

int head[MAXN],size[MAXN],dep[MAXN],father[MAXN],son[MAXN],seg[MAXN],rev[MAXN],top[MAXN],val[MAXN];
int lc[MAXN],rc[MAXN],mark[MAXN],sum[MAXN],color[2],last[2],L,R,cl,cr;
int n,m,tot;

void add(int u,int v)
{
	e[++tot].v = v;
	e[tot].next = head[u];
	head[u] = tot;
}

void dfs1(int u,int f)
{
	father[u] = f;
	size[u] = 1;
	dep[u] = dep[f] + 1;
	for(int i = head[u];i;i = e[i].next)
	{
		int v = e[i].v;
		if(!dep[v])
		{
			dfs1(v,u);
			size[u] += size[v];
			if(size[v] > size[son[u]])son[u] = v;
		}
	}
}

void dfs2(int u)
{
	if(son[u])
	{
		seg[son[u]] = ++seg[0];
		rev[seg[0]] = son[u];
		top[son[u]] = top[u];
		dfs2(son[u]);
	}
	for(int i = head[u];i;i = e[i].next)
	{
		int v = e[i].v;
		if(!seg[v])
		{
			seg[v] = ++seg[0];
			rev[seg[0]] = v;
			top[v] = v;
			dfs2(v);
		}
	}
}

void build(int k,int l,int r)
{
	mark[k] = -1;
	if(l == r)
	{
		lc[k] = rc[k] = val[rev[l]];
		sum[k] = 1;	
		return;
	}
	int mid = (l + r) >> 1;
	build(k << 1,l,mid);
	build(k << 1|1,mid + 1,r);
	if(rc[k << 1] != lc[k << 1|1])sum[k] = sum[k << 1] + sum[k << 1|1];
	else sum[k] = sum[k << 1] + sum[k << 1|1] - 1;
	lc[k] = lc[k << 1];
	rc[k] = rc[k << 1|1];
}

void pushdown(int k,int c)
{
	mark[k] = c;
	lc[k] = rc[k] = c;
	sum[k] = 1;
}

void charge(int k,int l,int r,int x,int y,int c)
{
	if(l >= x && r <= y)
	{
		mark[k] = c;
		sum[k] = 1;
		lc[k] = rc[k] = c;
		return;
	}
	int mid = (l + r) >> 1;
	if(mark[k] != -1)
	{
		pushdown(k << 1,mark[k]);
		pushdown(k << 1|1,mark[k]);
		mark[k] = -1;
	}
	if(x <= mid)charge(k << 1,l,mid,x,y,c);
	if(mid < y)charge(k << 1|1,mid + 1,r,x,y,c);
	if(rc[k << 1] != lc[k << 1|1])sum[k] = sum[k << 1] + sum[k << 1|1];
	else sum[k] = sum[k << 1] + sum[k << 1|1] - 1;
	lc[k] = lc[k << 1];
	rc[k] = rc[k << 1|1];
}
		

void change(int u,int v,int c)
{
	int fu = top[u];
	int fv = top[v];
	while(fu != fv)
	{
		if(dep[fu] < dep[fv])swap(u,v),swap(fu,fv);
		charge(1,1,n,seg[fu],seg[u],c);
		u = father[fu];
		fu = top[u];
	}
	if(seg[u] > seg[v])swap(u,v);
	charge(1,1,n,seg[u],seg[v],c);
}

int query(int k,int l,int r,int x,int y)
{
	int ans = 0;
	if(l >= x && r <= y)
	{
		if(L > l)
		{
			L = l;
			cl = lc[k];
			//cout << "l" << lc[k] << endl;
		}
		if(R < r)
		{
			R = r;
			cr = rc[k];
			//cout << "r" << rc[k] << endl;
		}
		return sum[k];
	}
	int mid = (l + r) >> 1;
	if(mark[k] != -1)
	{
		pushdown(k << 1,mark[k]);
		pushdown(k << 1|1,mark[k]);
		mark[k] = -1;
	}
	int right,left;
	left = right = 0;
	if(x <= mid)
	{
		ans += query(k << 1,l,mid,x,y);
	//	cout << l << ' ' << mid << ' ' << ans << endl;
		right = rc[k << 1];
	}
	if(mid < y)
	{
		ans += query(k << 1|1,mid + 1,r,x,y);
	//	cout << mid + 1 << ' ' << r << ' ' << ans << endl;
		left = lc[k << 1|1];
	}
	if(left & right)
	{
		if(right == left)
		{
			ans--;
			//cout << l << ' ' << r << endl;
		}
	}
	if(rc[k << 1] != lc[k << 1|1])sum[k] = sum[k << 1] + sum[k << 1|1];
	else sum[k] = sum[k << 1] + sum[k << 1|1] - 1;
	lc[k] = lc[k << 1];
	rc[k] = rc[k << 1|1];
	return ans;
}

int check(int u,int v)
{
	int fu = top[u];
	int fv = top[v];
	int ans = 0;
	int k = 0;
	while(fu != fv)
	{
		if(dep[fu] < dep[fv])swap(u,v),swap(fu,fv),k ^= 1;
		L = INF;
		R = 0;
		cl = -1;
		cr = -1;
		ans += query(1,1,n,seg[fu],seg[u]);
		if(cr == color[k])ans--;
	//	cout << seg[fu] << ' ' << seg[u] << ' ' << ans << endl;
		u = father[fu];
		fu = top[u];
		last[k] = L;
		color[k] = cl;
	}
	L = INF;
	R = 0;
	cl = -1;
	cr = -1;
	if(seg[u] > seg[v])swap(u,v);
	ans += query(1,1,n,seg[u],seg[v]);
	int opt;
	if(last[0] > last[1])opt = 1;
	else opt = 0;
	if(cl == color[opt])ans--;
	if(cr == color[opt^1])ans--;
	color[0] = color[1] = last[0] = last[1] = 0;
	return ans;
}

int main()
{
	scanf("%d%d",&n,&m);
	for(int i = 1;i <= n;i += 1)
		scanf("%d",&val[i]);
	for(int i = 1,u,v;i <= n - 1;i += 1)
	{
		scanf("%d%d",&u,&v);
		add(u,v);
	}
	dfs1(1,0);
	rev[1] = seg[0] = seg[1] = top[1] = 1;
	dfs2(1);
	build(1,1,n);
	/*cout << "seg:";
	for(int i = 1;i <= n;i += 1)	
		cout << seg[i] << ' ';*/
	string s;
	for(int i = 1,u,v,c;i <= m;i += 1)
	{
		cin >> s;
		if(s[0] == 'C')
		{
			scanf("%d%d%d",&u,&v,&c);
			change(u,v,c);
		}
		else {
			scanf("%d%d",&u,&v);
			printf("%d\n",check(u,v));
		}
	}
	return 0;
}