<p>Given an integer array <code>nums</code>, return <em>the number of <strong>reverse pairs</strong> in the array</em>.</p>

<p>A <strong>reverse pair</strong> is a pair <code>(i, j)</code> where:</p>

<ul>
	<li><code>0 &lt;= i &lt; j &lt; nums.length</code> and</li>
	<li><code>nums[i] &gt; 2 * nums[j]</code>.</li>
</ul>

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

<pre>
<strong>Input:</strong> nums = [1,3,2,3,1]
<strong>Output:</strong> 2
<strong>Explanation:</strong> The reverse pairs are:
(1, 4) --&gt; nums[1] = 3, nums[4] = 1, 3 &gt; 2 * 1
(3, 4) --&gt; nums[3] = 3, nums[4] = 1, 3 &gt; 2 * 1
</pre>

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

<pre>
<strong>Input:</strong> nums = [2,4,3,5,1]
<strong>Output:</strong> 3
<strong>Explanation:</strong> The reverse pairs are:
(1, 4) --&gt; nums[1] = 4, nums[4] = 1, 4 &gt; 2 * 1
(2, 4) --&gt; nums[2] = 3, nums[4] = 1, 3 &gt; 2 * 1
(3, 4) --&gt; nums[3] = 5, nums[4] = 1, 5 &gt; 2 * 1
</pre>

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

<ul>
	<li><code>1 &lt;= nums.length &lt;= 5 * 10<sup>4</sup></code></li>
	<li><code>-2<sup>31</sup> &lt;= nums[i] &lt;= 2<sup>31</sup> - 1</code></li>
</ul>

class BIT:
    def __init__(self, n):
        self.n = n
        self.tree = [0] * (n + 1)

    def update(self, index, value):
        while index <= self.n:
            self.tree[index] += value
            index += index & -index

    def query(self, index):
        result = 0
        while index > 0:
            result += self.tree[index]
            index -= index & -index
        return result

    def range_query(self, left, right):
        return self.query(right) - self.query(left - 1)


class Solution:
    def reversePairs(self, nums: List[int]) -> int:
        result = 0; unique_values = sorted(list(set(nums))); nu = len(unique_values)
        bit = BIT(nu); vmap = dict()
        for i, v in enumerate(unique_values): vmap[v] = i + 1
        print("Ue")
        for num in nums: print("Me"); bit.update(vmap[num], 1)
        for num in nums:
            bit.update(vmap[num], -1)
            index = bisect_left(unique_values, num / 2) - 1
            if index == -1: continue
            result += bit.query(vmap[unique_values[index]])
        return result
27500