只A了一个点，蒟蒻求助

RT

#include <bits/stdc++.h>
#define int long long
using namespace std;
const int maxn = 1000010;
int n,m,r,p;
int wt[maxn],head[maxn],deep[maxn],weight[maxn],
id[maxn],wson[maxn],fa[maxn],val[maxn],top[maxn];
int tot,cnt,res;

struct edge{
    int next,to,from,w,bel;
}e[maxn],ed[maxn];

struct segTree{
    int l,r,sum,tag;
}st[maxn]; 
//加边 
void adde(int a,int b){
    e[++tot].to = b;
    e[tot].next = head[a];
    e[tot].from = a;
    head[a] = tot;
    e[++tot].to = a;
    e[tot].next = head[b];
    e[tot].from = b;
    head[b] = tot;
}

void dfs1(int x,int f,int dep)
{
    fa[x] = f;
    deep[x] = dep;
    weight[x] = 1;
    int maxx = -1;
    for(int i = head[x]; i; i = e[i].next)
    {
        int y = e[i].to;
        if(y == f) continue;
        dfs1(y,x,dep + 1);
        weight[x] += weight[y];
        if(weight[y] > maxx)
        {
            maxx = weight[y];
            wson[x] = y;
        }
    }
    return ;
}

void dfs2(int x,int topf)
{
    id[x] = ++cnt;
    wt[cnt] = val[x];
    top[x] = topf;
    if(!wson[x]) return ;
    dfs2(wson[x],topf);
    for(int i = head[x]; i; i = e[i].next)
    {
        int y = e[i].to;
        if(!id[y]) dfs2(y,y);
    }
    return ;
}

void build(int now,int l,int r)
{
    st[now].l = l;
    st[now].r = r;
    if(l == r)
    {
        st[now].sum = wt[l];
        return ;
    }
    int mid = (l + r) / 2;
    build(now * 2,l,mid);
    build(now * 2 + 1,mid + 1,r);
    st[now].sum = max(st[now * 2].sum,st[now * 2 + 1].sum);
    return ;
}

void spread(int now)
{
    if(!st[now].tag) return ;
    int ls = now * 2,rs = now * 2 + 1;
    st[ls].sum += st[now].tag * (st[ls].r - st[ls].l + 1);
    st[rs].sum += st[now].tag * (st[rs].r - st[rs].l + 1);
    st[ls].tag += st[now].tag;
    st[rs].tag += st[now].tag;
    st[now].tag = 0;
    return ;
}

void add(int now,int l,int r,int k)
{
    if(l <= st[now].l && r >= st[now].r)
    {
        st[now].sum += k * (st[now].r - st[now].l + 1);
        st[now].tag += k;
        return ;
    }
    spread(now);
    int mid = (st[now].l + st[now].r) / 2;
    if(l <= mid) add(now * 2,l,r,k);
    if(r > mid) add(now * 2 + 1,l,r,k);
    st[now].sum = max(st[now * 2].sum,st[now * 2 + 1].sum);
    return ;
}

int query(int now,int l,int r)
{
    if(l <= st[now].l && r >= st[now].r) return st[now].sum;
    spread(now);
    int ans = 0;
    int mid = (st[now].l + st[now].r) / 2;
    if(l <= mid) ans = max(ans,query(now * 2,l,r));
    if(r > mid) ans = max(ans,query(now * 2 + 1,l,r));
    return ans;
}

int qrange(int x,int y)
{
    int ans = 0;
    while(top[x] != top[y])
    {
        if(deep[top[x]] < deep[top[y]]) swap(x,y);
        ans = max(ans,query(1,id[top[x]],id[x]));
        x = fa[top[x]];
    }
    if(deep[x] > deep[y]) swap(x,y);
    ans = max(ans,query(1,id[x] + 1,id[y]));
    return ans;
}

void updrange(int x,int y,int k)
{
    while(top[x] != top[y])
    {
        if(deep[top[x]] < deep[top[y]]) swap(x,y);
        add(1,id[top[x]],id[x],k);
        x = fa[top[x]];
    }
    if(deep[x] > deep[y]) swap(x,y);
    add(1,id[x] + 1,id[y],k);
}
signed main()
{
    scanf("%lld",&n);
    for(int i = 1; i < n; i++)
    {
        int x,y,z;
        scanf("%lld%lld%lld",&x,&y,&z);
        adde(x,y);
        ed[i].from = x,ed[i].to = y,ed[i].w = z;
    }
    dfs1(1,0,1);
    for(int i = 1; i < n; i++)
    {
        int x = ed[i].from,y = ed[i].to;
        if(deep[x] < deep[y]) val[y] = ed[i].w,ed[i].bel = y;
        else val[x] = ed[i].w,ed[i].bel = x;
    }
    dfs2(1,1);
    build(1,1,n);
    while(1)
    {
        string op;
        cin >> op;
        if(op == "DONE") break;
        if(op == "QUERY")
        {
            int x,y;
            scanf("%lld%lld",&x,&y);
            printf("%lld\n",qrange(x,y));
        }
        if(op == "CHANGE")
        {
            int x,y;
            scanf("%lld%lld",&x,&y);
            int pp = ed[x].bel;
            add(1,id[pp],id[pp],y - val[pp]);
            //updrange(x,x,y - val[x]);
        }
    }
    return 0;
}