看起来就是个树链剖分的题...

https://vijos.org/p/1986

所以直接树链剖分剖一下就好了..

所以写的好长啊..

代码:

#include<set>
#include<map>
#include<list>
#include<queue>
#include<stack>
#include<string>
#include<time.h>
#include<math.h>
#include<memory>
#include<vector>
#include<bitset>
#include<fstream>
#include<stdio.h>
#include<utility>
#include<sstream>
#include<string.h>
#include<iostream>
#include<stdlib.h>
#include<algorithm>
using namespace std;
int a[100005];
struct edge
{
    int y;
    edge * next;
};
edge * li[100005];
edge * new_edge()
{
    static edge a[200005];
    static int top=0;
    return &a[top++];
}
void inserts(int x,int y)
{
    edge * t=new_edge();
    t->y=y;
    t->next=li[x];
    li[x]=t;
}
void insert_edge(int x,int y)
{
    inserts(x,y);
    inserts(y,x);
}
edge * prefer[100005];
int dfn[100005];
int father[100005];
int size[100005];
int depth[100005];
int vis[100005];
void dfs1(int x)
{
    size[x]=1;
    edge * t;
    int max_weight=0;
    for (t=li[x];t!=0;t=t->next)
    {
        if (t->y==father[x]) continue;
        father[t->y]=x;
        depth[t->y]=depth[x]+1;
        dfs1(t->y);
        size[x]+=size[t->y];
        if (size[t->y]>max_weight)
        {
            max_weight=size[t->y];
            prefer[x]=t;
        }
    }
}
int up[100005];
void dfs2(int x)
{
    static int num=0;
    dfn[x]=num;
    vis[num]=x;
    num++;
    if (prefer[x]==0) return;
    up[prefer[x]->y]=up[x];
    dfs2(prefer[x]->y);
    edge * t;
    for (t=li[x];t!=0;t=t->next)
    {
        if (t==prefer[x]) continue;
        if (t->y==father[x]) continue;
        up[t->y]=t->y;
        dfs2(t->y);
    }
}
int val[1<<18];
void build_tree(int num,int l,int r)
{
    if (l==r-1)
    {
        val[num]=a[vis[l]];
        return;
    }
    int mid=(l+r)/2;
    build_tree(num*2+1,l,mid);
    build_tree(num*2+2,mid,r);
    val[num]=val[num*2+1]+val[num*2+2];
}
void change(int num,int l,int r,int k,int t)
{
    if (l==r-1)
    {
        val[num]=t;
        return;
    }
    int mid=(l+r)/2;
    if (k<mid) change(num*2+1,l,mid,k,t);
    else change(num*2+2,mid,r,k,t);
    val[num]=val[num*2+1]+val[num*2+2];
}
int query(int num,int l,int r,int l0,int r0)
{
    if ((l0<=l)&&(r<=r0))
    {
        return val[num];
    }
    int mid=(l+r)/2;
    int sum=0;
    if (l0<mid) sum+=query(num*2+1,l,mid,l0,r0);
    if (mid<r0) sum+=query(num*2+2,mid,r,l0,r0);
    return sum;
}
int main()
{
    #ifdef absi2011
    freopen("input.txt","r",stdin);
    freopen("output.txt","w",stdout);
    #endif
    int n;
    scanf("%d",&n);
    int i;
    for (i=0;i<n;i++)
    {
        scanf("%d",&a[i]);
    }
    for (i=1;i<n;i++)
    {
        int x,y;
        scanf("%d%d",&x,&y);
        x--;
        y--;
        insert_edge(x,y);
    }
    depth[0]=0;
    father[0]=-1;
    dfs1(0);
    up[0]=0;
    dfs2(0);
    build_tree(0,0,n);
    int m;
    scanf("%d",&m);
    for (i=0;i<m;i++)
    {
        static char oper[5];
        scanf("%s",oper);
        int x,y;
        scanf("%d%d",&x,&y);
        if (oper[0]=='C')
        {
            x--;
            change(0,0,n,dfn[x],y);
        }
        else
        {
            x--;
            y--;
            int sum=0;
            for (;;)
            {
                if (up[x]==up[y])
                {
                    if (depth[x]<depth[y]) swap(x,y);
                    sum+=query(0,0,n,dfn[y],dfn[x]+1);
                    break;
                }
                else
                {
                    if (depth[up[x]]<depth[up[y]]) swap(x,y);
                    sum+=query(0,0,n,dfn[up[x]],dfn[x]+1);
                    x=father[up[x]];
                }
            }
            printf("%d\n",sum);
        }
    }
    return 0;
}