蒟蒻刚学树链剖分，求助

#include <iostream>
#include <cstring>
#include <cstdio>
#include <algorithm>
#define ls (u << 1)
#define rs (u << 1 | 1)

using namespace std;

const int N = 2e5 + 5, INF = 1e9 + 18;

int n, m;
int h[N], ne[N], e[N], idx;
int w[N], nw[N];
int sz[N], dep[N], top[N], cnt, fa[N], son[N], id[N];
struct node {
    int l, r;
    int maxx, minn, lmax, rmax;
    int lazy;
}tr[N * 4];

void add_edge(int a, int b) {
    ne[idx] = h[a], e[idx] = b, h[a] = idx ++;
}

void dfs1(int u, int father, int depth) {
    dep[u] = depth, fa[u] = father, sz[u] = 1;
    for(int i = h[u]; ~i; i = ne[i]) {
        int j = e[i];
        if(j == father) continue;
        dfs1(j, u, depth + 1);
        sz[u] += sz[j];
        if(sz[j] > sz[son[u]]) son[u] = j;
    }
}

void dfs2(int u, int t) {
    id[u] = ++ cnt, nw[cnt] = w[u], top[u] = t;
    if(!son[u]) return;
    dfs2(son[u], t);
    for(int i = h[u]; ~i; i = ne[i]) {
        int j = e[i];
        if(j == fa[u] || j == son[u]) continue;
        dfs2(j, j);
    }
}

void pushup(int u) {
    tr[u].maxx = max(tr[ls].maxx, tr[rs].maxx);
    tr[u].minn = min(tr[ls].minn, tr[rs].minn);
    tr[u].lmax = max(tr[ls].maxx - tr[rs].minn, max(tr[ls].lmax, tr[rs].lmax));//向左走
    tr[u].rmax = max(tr[rs].maxx - tr[ls].minn, max(tr[ls].rmax, tr[rs].rmax));//向右走
}

void add(int u, int v) {
    tr[u].lazy += v, tr[u].maxx += v, tr[u].minn += v;
}

void pushdown(int u) {
    if(tr[u].lazy) {
        add(ls, tr[u].lazy), add(rs, tr[u].lazy);
        tr[u].lazy = 0;
    }
}

node merge(node L, node R) {
    node res;
    res.maxx = max(L.maxx, R.maxx);
    res.minn = min(L.minn, R.minn);
    res.lmax = max(L.maxx - R.minn, max(L.lmax, R.lmax));
    res.rmax = max(R.maxx - L.minn, max(L.rmax, R.rmax));
    return res;
}

void build(int u, int l, int r) {
    tr[u] = {l, r, nw[l], nw[l]};
    if(l == r) return;
    int mid = l + r >> 1;
    build(ls, l, mid), build(rs, mid + 1, r);
    pushup(u);
}

void update(int u, int l, int r, int v) {
    if(l <= tr[u].l && tr[u].r <= r) {
        add(u, v);
        return;
    }
    pushdown(u);
    int mid = tr[u].l + tr[u].r >> 1;
    if(l <= mid) update(ls, l, r, v);
    if(r > mid) update(rs, l, r, v);
    pushup(u);
}

node query(int u, int l, int r) {
    if(l <= tr[u].l && tr[u].r <= r) {
        return tr[u];
    }
    pushdown(u);
    int mid = tr[u].l + tr[u].r >> 1;
    if(r <= mid) return query(ls, l, r);
    if(l > mid) return query(rs, l, r);
    return merge(query(ls, l, r), query(rs, l, r));
}

void update_path(int x, int y, int v) {
    while(top[x] != top[y]) {
        if(dep[top[x]] < dep[top[y]]) swap(x, y);
        update(1, id[top[x]], id[x], v);
        x = fa[top[x]];
    }
    if(dep[x] < dep[y]) swap(x, y);
    update(1, id[y], id[x], v);
}

int query_path(int x, int y) {
    node l, r;
    l.minn = r.minn = INF;
    while(top[x] != top[y]) {
        if(dep[top[x]] < dep[top[y]]) {
            r = merge(query(1, id[top[y]], id[y]), r);
            y = fa[top[y]];
        }
        else {
            l = merge(l, query(1, id[top[x]], id[x]));
            x = fa[top[x]];
        }
    }
    if(dep[x] > dep[y]) l = merge(l, query(1, id[y], id[x]));
    else r = merge(query(1, id[x], id[y]), r);
    return merge(l, r).rmax;
}

int main() {
    
    memset(h, -1, sizeof h);
    cin >> n;
    
    for(int i = 1; i <= n; ++ i) cin >> w[i];
    
    for(int i = 0; i < n - 1; ++ i) {
        int a, b;
        cin >> a >> b;
        add_edge(a, b), add_edge(b, a);
    }
    
    dfs1(1, -1, 1);
    dfs2(1, 1);
    build(1, 1, n);
    
    cin >> m;
    
    while(m -- ) {
        int a, b, c;
        cin >> a >> b >> c;
        cout << query_path(a, b) << endl;
        update_path(a, b, c);
    }
    
    return 0;
}