<p>Given an integer array <code>nums</code> and two integers <code>lower</code> and <code>upper</code>, return <em>the number of range sums that lie in</em> <code>[lower, upper]</code> <em>inclusive</em>.</p>

<p>Range sum <code>S(i, j)</code> is defined as the sum of the elements in <code>nums</code> between indices <code>i</code> and <code>j</code> inclusive, where <code>i &lt;= j</code>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> nums = [-2,5,-1], lower = -2, upper = 2
<strong>Output:</strong> 3
<strong>Explanation:</strong> The three ranges are: [0,0], [2,2], and [0,2] and their respective sums are: -2, -1, 2.
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> nums = [0], lower = 0, upper = 0
<strong>Output:</strong> 1
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= nums.length &lt;= 10<sup>5</sup></code></li>
	<li><code>-2<sup>31</sup> &lt;= nums[i] &lt;= 2<sup>31</sup> - 1</code></li>
	<li><code>-10<sup>5</sup> &lt;= lower &lt;= upper &lt;= 10<sup>5</sup></code></li>
	<li>The answer is <strong>guaranteed</strong> to fit in a <strong>32-bit</strong> integer.</li>
</ul>

#include <iostream>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#include <vector>

using namespace __gnu_pbds;
using namespace std;

typedef tree<
    pair<long long, int>, // Pair of (value, unique identifier)
    null_type,
    less<pair<long long, int>>, // Comparator
    rb_tree_tag,
    tree_order_statistics_node_update // Updates the structure with each insert/delete
> ordered_set;

class Solution {
public:
    long long func(vector<int>& nums, long long val) {
        int n = nums.size();
        long long sm = 0;
        ordered_set os;
        long long ans = 0;
        for (int i = 0; i < n; i++) {
            sm += nums[i];
            long long k = sm - val;
            int cnt = os.order_of_key({k, INT_MIN});
            ans += os.size() - cnt;
            if (sm <= val) ans++;
            os.insert({sm, i});
        }
        return ans;
    }

    int countRangeSum(vector<int>& nums, int lower, int upper) {
        return func(nums, upper) - func(nums, lower - 1);
    }
};

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