維護區間左顏色值，右顏色值，顏色段個數。

#include <iostream>
#include <cstdio>
using namespace std;
int n, m, uu, vv, ww, w[100005], wt[100005], qwq, idx[100005], hea[100005];
int cnt, dep[100005], siz[100005], son[100005], fa[100005], top[100005];
char ss[15];
struct Edge{
    int too, nxt;
}edge[200005];
struct SGT{
    int col[400005], lco[400005], rco[400005
 
], tag[400005];
    void upd(int o, int lson, int rson){
        col[o] = col[lson] + col[rson];
        if(rco[lson]==lco[rson])    col[o]--;
        lco[o] = lco[lson];
        rco[o] = rco[rson];
    }
    void build(int o, int l, int r){
        if(l==r)    lco[o] = rco[o] = wt[l], col[o] = 1;
        else
 
{
            int mid=(l+r)>>1;
            int lson=o<<1;
            int rson=lson|1;
            if(l<=mid)  build(lson, l, mid);
            if(mid<r)   build(rson, mid+1, r);
            upd(o, lson, rson);
        }
    }
    void pushDown(int o, int l, int r, int lson, int rson, int
 
 mid){
        col[lson] = col[rson] = 1;
        lco[lson] = rco[lson] = lco[rson] = rco[rson] = tag[o];
        tag[lson] = tag[rson] = tag[o];
        tag[o] = 0;
    }
    void update(int o, int l, int r, int x, int y, int k){
        if(l>=x && r<=y){
            col[o] = 1;
            lco[o] = rco[o] = tag[o] = k;
        }
        else{
            int mid=(l+r)>>1;
            int lson=o<<1;
            int rson=lson|1;
            if(tag[o])  pushDown(o, l, r, lson, rson, mid);
            if(x<=mid)  update(lson, l, mid, x, y, k);
            if(mid<y)   update(rson, mid+1, r, x, y, k);
            upd(o, lson, rson);
        }
    }
    int query(int o, int l, int r, int x, int y){
        if(l>=x && r<=y)    return col[o];
        else{
            int mid=(l+r)>>1;
            int lson=o<<1;
            int rson=lson|1;
            int ans=0;
            if(tag[o])  pushDown(o, l, r, lson, rson, mid);
            if(x<=mid)  ans += query(lson, l, mid, x, y);
            if(mid<y)   ans += query(rson, mid+1, r, x, y);
            if(x<=mid && mid<y && rco[lson]==lco[rson]) return ans-1;
            return ans;
        }
    }
    int queryCol(int o, int l, int r, int x){
        if(l==r)    return lco[o];
        else{
            int mid=(l+r)>>1;
            int lson=o<<1;
            int rson=lson|1;
            if(tag[o])  pushDown(o, l, r, lson, rson, mid);
            if(x<=mid)  return queryCol(lson, l, mid, x);
            else    return queryCol(rson, mid+1, r, x);
        }
    }
}sgt;
void add_edge(int fro, int too){
    edge[++cnt].nxt = hea[fro];
    edge[cnt].too = too;
    hea[fro] = cnt;
}
void dfs1(int x, int f){
    dep[x] = dep[f] + 1;
    siz[x] = 1;
    fa[x] = f;
    int maxSon=-1;
    for(int i=hea[x]; i; i=edge[i].nxt){
        int t=edge[i].too;
        if(t!=f){
            dfs1(t, x);
            siz[x] += siz[t];
            if(maxSon<siz[t])   maxSon = siz[t], son[x] = t;
        }
    }
}
void dfs2(int x, int topf){
    top[x] = topf;
    idx[x] = ++qwq;
    wt[qwq] = w[x];
    if(!son[x]) return ;
    dfs2(son[x], topf);
    for(int i=hea[x]; i; i=edge[i].nxt){
        int t=edge[i].too;
        if(t!=fa[x] && t!=son[x])
            dfs2(t, t);
    }
}
void changeRange(int uu, int vv, int ww){
    while(top[uu]!=top[vv]){
        if(dep[top[uu]]<dep[top[vv]])   swap(uu, vv);
        sgt.update(1, 1, n, idx[top[uu]], idx[uu], ww);
        uu = fa[top[uu]];
    }
    if(dep[uu]>dep[vv]) swap(uu, vv);
    sgt.update(1, 1, n, idx[uu], idx[vv], ww);
}
int queryRange(int uu, int vv){
    int ans=0, orz, sto;
    while(top[uu]!=top[vv]){
        if(dep[top[uu]]<dep[top[vv]])   swap(uu, vv);
        ans += sgt.query(1, 1, n, idx[top[uu]], idx[uu]);
        orz = sgt.queryCol(1, 1, n, idx[top[uu]]);
        sto = sgt.queryCol(1, 1, n, idx[fa[top[uu]]]);
        if(orz==sto)    ans--;
        uu = fa[top[uu]];
    }
    if(dep[uu]>dep[vv]) swap(uu, vv);
    ans += sgt.query(1, 1, n, idx[uu], idx[vv]);
    return ans;
}
int main(){
    cin>>n>>m;
    for(int i=1; i<=n; i++) scanf("%d", &w[i]);
    for(int i=1; i<n; i++){
        scanf("%d %d", &uu, &vv);
        add_edge(uu, vv);
        add_edge(vv, uu);
    }
    dfs1(1, 0);
    dfs2(1, 1);
    sgt.build(1, 1, n);
    while(m--){
        scanf("%s", ss);
        if(ss[0]==‘C‘){
            scanf("%d %d %d", &uu, &vv, &ww);
            changeRange(uu, vv, ww);
        }
        else{
            scanf("%d %d", &uu, &vv);
            printf("%d\n", queryRange(uu, vv));
        }
    }
    return 0;
}

luogu2486 [SDOI2011]染色