Сжатое ДО (Плюс в точке и сумма)

#include <bits/stdc++.h>

using namespace std;

#define ll long long

struct node
{
    node *l, *r;
    int key, tl, tr;
    node(int _tl, int _tr)
    {
        l = r = nullptr, key = 0, tl = _tl, tr = _tr;
    }
};

int get_key(node * a)
{
    if (a == nullptr)
        return 0;
    return a->key;
}

void modify(node * cur, int pos, int val)
{
    if (cur->tl + 1 == cur->tr)
    {
        cur->key += val;
        return;
    }
    int m = (cur->tl + cur->tr) / 2;
    if (pos < m)
    {
        if (cur->l == nullptr) cur->l = new node(cur->tl, m);
        modify(cur->l, pos, val);
    }
    else
    {
        if (cur->r == nullptr) cur->r = new node(m, cur->tr);
        modify(cur->r, pos, val);
    }
    cur->key = get_key(cur->l) + get_key(cur->r);
}

int get_sum(node * cur, int l, int r)
{
    if (cur == nullptr)
        return 0;
    if (l <= cur->tl && cur->tr <= r)
    {
        return cur->key;
    }
    else if (l >= cur->tr || cur->tl >= r)
    {
        return 0;
    }
    int m = (cur->tl + cur->tr) / 2;
    return get_sum(cur->l, l, r) + get_sum(cur->r, l, r);
}

int main()
{
    ios::sync_with_stdio(0);
    cin.tie(0);
    node * tree = new node(-10, 10);
    modify(tree, 0, 3);
    modify(tree, -3, 6);
    cout << get_sum(tree, -10, 10) << ' ' << get_sum(tree, -3, -2) << '\n';
    return 0;
}