<p>Given an integer array <code>nums</code>, return<em> an integer array </em><code>counts</code><em> where </em><code>counts[i]</code><em> is the number of smaller elements to the right of </em><code>nums[i]</code>.</p>

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

<pre>
<strong>Input:</strong> nums = [5,2,6,1]
<strong>Output:</strong> [2,1,1,0]
<strong>Explanation:</strong>
To the right of 5 there are <b>2</b> smaller elements (2 and 1).
To the right of 2 there is only <b>1</b> smaller element (1).
To the right of 6 there is <b>1</b> smaller element (1).
To the right of 1 there is <b>0</b> smaller element.
</pre>

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

<pre>
<strong>Input:</strong> nums = [-1]
<strong>Output:</strong> [0]
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> nums = [-1,-1]
<strong>Output:</strong> [0,0]
</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>-10<sup>4</sup> &lt;= nums[i] &lt;= 10<sup>4</sup></code></li>
</ul>

class SegmentTree:
    def __init__(self):
        self.size = 2 * 10**4 + 1
        self.tree = [0] * (4 * self.size)

    def query(self, treeIndex, left, right, i, j):
        if i > right or j < left:
            return 0
        if i <= left and j >= right:
            return self.tree[treeIndex]
        mid = (left + right) // 2
        leftQuery = self.query(2 * treeIndex + 1, left, mid, i, j)
        rightQuery = self.query(2 * treeIndex + 2, mid + 1, right, i, j)
        return leftQuery + rightQuery
        
    def update(self, treeIndex, left, right, i):
        if left == right:
            self.tree[treeIndex] += 1
            return
        mid = (left + right) // 2
        if i > mid:
            self.update(2 * treeIndex + 2, mid + 1, right, i)
        else:
            self.update(2 * treeIndex + 1, left, mid, i)
        self.tree[treeIndex] = self.tree[2 * treeIndex + 1] + self.tree[2 * treeIndex + 2]


class Solution:
    def countSmaller(self, nums: List[int]) -> List[int]:
        tree = SegmentTree()
        offset = 10 ** 4
        ans = []
        for num in nums[::-1]:
            ans.append(tree.query(0, 0, tree.size - 1, 0, num + offset - 1))
            tree.update(0, 0, tree.size - 1, num + offset)
        return ans[::-1]
3695