样例输入到 QMAX 3 2 的时候就卡住停止了，不知道怎么回事

#include <bits/stdc++.h> 
using namespace std;
#define lc id << 1
#define rc id << 1 | 1
const int maxn = 6e4 + 1;
const int inf = 2e9;
int cur, cnt, n, q;
int h[maxn], p[maxn], nxt[maxn];
int w[maxn];
int son[maxn], siz[maxn], dep[maxn], top[maxn], dfn[maxn], fa[maxn], rnk[maxn];
void add_edge(int x, int y) {
    cur++;
    nxt[cur] = h[x];
    h[x] = cur;
    p[cur] = y;
}
struct seg {
    int sum[maxn * 2], maxx[maxn * 2];
    void maintain(int id) {
        sum[id] = sum[lc] + sum[rc];
        maxx[id] = max(maxx[lc], maxx[rc]);
    }
    void build(int id, int l, int r) {
        if(l == r) {
            sum[id] = maxx[id] = w[rnk[l]];
            return;
        }
        int mid = l + r >> 1;
        build(lc, l, mid);
        build(rc, mid + 1, r);
        maintain(id);
    }
    int qrymax(int id, int l, int r, int ql, int qr) {
        if(l > qr || r < ql) return -inf;
        if(ql <= l && qr <= r) return maxx[id];
        int mid = l + r >> 1;
        return max(qrymax(lc, l, mid, ql, qr), 
            qrymax(rc, mid + 1, r, ql, qr));
    }
    int qrysum(int id, int l, int r, int ql, int qr) {
        if(l > qr || r < ql) return 0;
        if(ql <= l && qr <= r) return sum[id];
        int mid = l + r >> 1;
        return qrysum(lc, l, mid, ql, qr) + 
            qrysum(rc, mid + 1, r, ql, qr);
    }
    void update(int id, int l, int r, int x, int t) {
        if(l == r) {
          maxx[id] = sum[id] = t;
          return;
        }
        int mid = l + r >> 1;
        if(x <= mid) update(lc, l, mid, x, t);
        else update(rc, mid + 1, r, x, t);
        maintain(id);
    }
} st;
int dfs1(int u, int depth) {
    son[u] = -1;
    siz[son[u]] = 0;
    dep[u] = depth;
    siz[u] = 1;
    for(int j = h[u]; j; j = nxt[j]) {
        int v = p[j];
        if(!dep[v]) {
            siz[u] += dfs1(v, depth + 1);
            fa[v] = u;
            if(son[u] == -1 || siz[v] > siz[son[u]])
                son[u] = v;     
        }
    }
    return siz[u];
}
void dfs2(int u, int tp) {
    top[u] = tp;
    cnt++;
    dfn[u] = cnt;
    rnk[cnt] = u;
    if(son[u] != -1) {
        dfs2(son[u], tp);
        for(int j = h[u]; j; j = nxt[j]) {
            if(p[j] != son[u] && p[j] != fa[u])
                dfs2(p[j], p[j]);
        }
    }
}
int getmax(int x, int y) {
    int ret = -inf;
    int fx = top[x];
    int fy = top[y];
    while(fx != fy) {
        if(dep[fx] >= dep[fy]) {
            ret = max(ret, st.qrymax(1, 1, n, dfn[fx], dfn[x]));
            x = fa[fx];
        }
        else {
            ret = max(ret, st.qrymax(1, 1, n, dfn[fy], dfn[y]));
            y = fa[fy];
        }
        fx = top[x], fy = top[y];
    }
    int mn = min(dfn[x], dfn[y]);
    int mx = max(dfn[x], dfn[y]);
    return max(ret, st.qrymax(1, 1, n, mn, mx));
}
int getsum(int x, int y) {
    int ret = 0;
    int fx = top[x];
    int fy = top[y];
    while(fx != fy) {
        if(dep[fx] >= dep[fy]) {
            ret += st.qrysum(1, 1, n, dfn[fx], dfn[x]);
            x = fa[fx];
        }
        else {
            ret += st.qrysum(1, 1, n, dfn[fy], dfn[y]);
            y = fa[fy];
        }
        fx = top[x], fy = top[y];
    }
    int mn = min(dfn[x], dfn[y]);
    int mx = max(dfn[x], dfn[y]);
    return ret + st.qrysum(1, 1, n, mn, mx);
}
int main() {
    cin >> n;
    for(int i = 1, x, y; i < n; i++) {
        cin >> x >> y;
        add_edge(x, y);
        add_edge(y, x);
    }
    for(int i = 1; i <= n; i++) cin >> w[i];
    dfs1(1, 1);
    dfs2(1, 1);
    st.build(1, 1, n);
    cin >> q;
    char op[10];
    int u, v;
    while(q--) {
        cin >> op >> u >> v;
        if(!strcmp(op, "CHANGE"))
            st.update(1, 1, n, dfn[u], v);
        else if(!strcmp(op, "CHANGE"))
            cout << getmax(u, v) << endl;
        else cout << getsum(u, v) << endl;
    }
    return 0;
}