题意：传送门

题解：使用树链剖分，参考传送门

附上代码(计划改一种代码风格)：

#include<iostream>
#include<cstdio>
using namespace std;
const int maxn=3e4+5;
const int maxm=6e4+5;
const int inf=0x7fffffff;
struct edge{int v,next;}e[maxm];
int head[maxn],tot;
void add_edges(int u,int v)
{
    e[++tot].v=v;e[tot].next=head[u];head[u]=tot;
    e[++tot].v=u;e[tot].next=head[v];head[v]=tot;
}
int n,q,v[maxn];
int size[maxn],dep[maxn],fa[maxn];
int sz,pos[maxn],bl[maxn];
void dfs1(int u)
{
    size[u]=1;
    for(int i=head[u];i;i=e[i].next)
    {
        if(e[i].v==fa[u])continue;
        dep[e[i].v]=dep[u]+1;
        fa[e[i].v]=u;
        dfs1(e[i].v);
        size[u]+=size[e[i].v];
    }
}
void dfs2(int u,int chain)
{
    int k=0;sz++;
    pos[u]=sz;
    bl[u]=chain;
    for(int i=head[u];i;i=e[i].next)
        if(dep[e[i].v]>dep[u]&&size[e[i].v]>size[k])
            k=e[i].v;
    if(k==0)return;
    dfs2(k,chain);
    for(int i=head[u];i;i=e[i].next)
        if(dep[e[i].v]>dep[u]&&k!=e[i].v)
            dfs2(e[i].v,e[i].v);
}
struct seg{int l,r,sum,mx;}t[100005];
void build(int k,int l,int r)
{
    t[k].l=l;t[k].r=r;
    if(l==r)return;
    int mid=(l+r)>>1;
    build(k<<1,l,mid);
    build(k<<1|1,mid+1,r);
}
void change(int k,int x,int y)
{
    int l=t[k].l,r=t[k].r,mid=(l+r)>>1;
    if(l==r){t[k].sum=t[k].mx=y;return;}
    if(x<=mid)change(k<<1,x,y);
    else change(k<<1|1,x,y);
    t[k].sum=t[k<<1].sum+t[k<<1|1].sum;
    t[k].mx=max(t[k<<1].mx,t[k<<1|1].mx);
}
int querysum(int k,int x,int y)
{
    int l=t[k].l,r=t[k].r,mid=(l+r)>>1;
    if(l==x&&y==r)return t[k].sum;
    if(y<=mid)return querysum(k<<1,x,y);
    else if(x>mid)return querysum(k<<1|1,x,y);
    else return querysum(k<<1,x,mid)+querysum(k<<1|1,mid+1,y);
}
int querymx(int k,int x,int y)
{
    int l=t[k].l,r=t[k].r,mid=(l+r)>>1;
    if(l==x&&y==r)return t[k].mx;
    if(y<=mid)return querymx(k<<1,x,y);
    else if(x>mid)return querymx(k<<1|1,x,y);
    else return max(querymx(k<<1,x,mid),querymx(k<<1|1,mid+1,y));
}
int solvesum(int x,int y)
{
    int sum=0;
    while(bl[x]!=bl[y])
    {
        if(dep[bl[x]]<dep[bl[y]])swap(x,y);
        sum+=querysum(1,pos[bl[x]],pos[x]);
        x=fa[bl[x]];
    }
    if(pos[x]>pos[y])swap(x,y);
    sum+=querysum(1,pos[x],pos[y]);
    return sum;
}
int solvemx(int x,int y)
{
    int mx=-inf;
    while(bl[x]!=bl[y])
    {
        if(dep[bl[x]]<dep[bl[y]])swap(x,y);
        mx=max(mx,querymx(1,pos[bl[x]],pos[x]));
        x=fa[bl[x]];
    }
    if(pos[x]>pos[y])swap(x,y);
    mx=max(mx,querymx(1,pos[x],pos[y]));
    return mx;
}
void solve()
{
    build(1,1,n);
    for(int i=1;i<=n;i++)
        change(1,pos[i],v[i]);
    scanf("%d",&q);
    char ch[10];
    for(int i=1;i<=q;i++)
    {
        int x,y;scanf("%s%d%d",ch,&x,&y);
        if(ch[0]=='C'){v[x]=y;change(1,pos[x],y);}
        else
        {
            if(ch[1]=='M')
                printf("%d\n",solvemx(x,y));
            else
                printf("%d\n",solvesum(x,y));
        }
    }
}
int main()
{
    scanf("%d",&n);
    for(int i=1;i<n;i++)
    {
        int x,y;
        scanf("%d%d",&x,&y);
        add_edges(x,y);
    }
    for(int i=1;i<=n;i++)scanf("%d",&v[i]);
    dfs1(1);
    dfs2(1,1);
    solve();
    return 0;
}