ll query(int rt, int l, int r, int pos) {
    if (l == r) {
        return val[rt];
    }
    pushdown(rt,l,r);
    int mid = l + r >> 1;
    if (pos <= mid) return query(rt << 1, l, mid, pos);
    else return query(rt << 1 | 1, mid + 1, r, pos);
}

为什么在查询的时候还要进行pushdown操作