萌新求助，树剖wa了八个点，看了半天没看出来

#include<bits/stdc++.h>
#define SIZE 300000
#define lson (p<<1)
#define rson (p<<1|1)
#define mid (l+r>>1)
using namespace std;
int n,m;
int Head[SIZE],Next[SIZE],Ver[SIZE];
int fa[SIZE],Deep[SIZE],Size[SIZE],Son[SIZE];
int tot=0;
int Top[SIZE];
int cnt;
int id[SIZE];
int wt[SIZE],w[SIZE];
int Max[SIZE],Sum[SIZE];
int res,ves;
void Add(int x,int y){
    Ver[++tot]=y;
    Next[tot]=Head[x];
    Head[x]=tot;
}
void dfs1(int x,int f,int deep){
    Deep[x]=deep;
    fa[x]=f;
    Size[x]=1;
    int maxson=-1;
    for(int i=Head[x];i;i=Next[i]){
        int y=Ver[i];
        if(y==f) continue;
        dfs1(y,x,deep+1);
        Size[x]+=Size[y];
        if(Size[y]>maxson) maxson=Size[y],Son[x]=y;
    }
}
void dfs2(int x,int topf){
    id[x]=++cnt;
    w[cnt]=wt[x];
    Top[x]=topf;
    if(!Son[x]) return;
    dfs2(Son[x],topf);
    for(int i=Head[x];i;i=Next[i]){
        int y=Ver[i];
        if(y==fa[x]||y==Son[x])continue;
        dfs2(y,y);
    }
}
void build(int p,int l,int r){
    if(l==r){
        Sum[p]=w[l];
        Max[p]=w[l];
        return;
    }
    build(lson,l,mid);
    build(rson,mid+1,r);
    Sum[p]=Sum[lson]+Sum[rson];
    Max[p]=max(Max[lson],Max[rson]);
}
void change(int p,int l,int r,int Val,int pos){
    if(pos>r||pos<l) return;
    if(l==r&&r==pos){
        Sum[p]=Val;
        Max[p]=Val;
        return;
    }
    if(mid>=pos) change(lson,l,mid,Val,pos);
    if(pos>=mid+1) change(rson,mid+1,r,Val,pos);
    Sum[p]=Sum[lson]+Sum[rson];
    Max[p]=max(Max[lson],Max[rson]);
}
void query(int p,int l,int r,int L,int R){
    if(L<=l&&r<=R){
        res+=Sum[p];
        ves=max(ves,Max[p]);
        return;
    }
    if(L<=mid) query(lson,l,mid,L,R);
    if(R>mid) query(rson,mid+1,r,L,R);
}
int QSUM(int x,int y){
    int ans=0;
    while(Top[x]!=Top[y]){
        res=0;
        if(Deep[Top[x]]<Deep[Top[y]]) swap(x,y);
        query(1,1,n,id[Top[x]],id[x]);
        ans+=res;
        x=fa[Top[x]];
    }
    if(Deep[x]>Deep[y]) swap(x,y);
    res=0;
    query(1,1,n,id[x],id[y]);
    ans+=res;
    return ans;
}
int QMAX(int x,int y){
    int ans=-300000;
    while(Top[x]!=Top[y]){
        if(Deep[Top[x]]<Deep[Top[y]]) swap(x,y);
        ves=-300000;
        query(1,1,n,id[Top[x]],id[x]);
        ans=max(ves,ans);
        x=fa[Top[x]];
    }
    if(Deep[x]>Deep[y]) swap(x,y);
    ves=-300000;
    query(1,1,n,id[x],id[y]);
    ans=max(ans,ves);
    return ans;
}
int main(){
    scanf("%d",&n);
    for(int i=1;i<=n-1;i++){
        int a,b;
        scanf("%d%d",&a,&b);
        Add(a,b);
        Add(b,a);
    }
    for(int i=1;i<=n;i++) scanf("%d",&wt[i]);
    scanf("%d",&m);
    dfs1(1,0,1);
    dfs2(1,1);
    build(1,1,n);
    while(m--){
        string order;
        int x,y;
        cin>>order;
        scanf("%d%d",&x,&y);
        if(order=="CHANGE") change(1,1,n,y,x);
        if(order=="QMAX") printf("%d\n",QMAX(x,y));
        if(order=="QSUM") printf("%d\n",QSUM(x,y));
    }
    return 0;
}