class Solution:
    def countSmaller(self, nums):
        class Node:
            def __init__(self, val):
                self.val = val
                self.left = None
                self.right = None
                self.count = 0
 
        def bst_insert(root, val, result, count):
            if not root:
                root = Node(val)
                result.append(count)
                return root
            if val > root.val:
                root.right = bst_insert(root.right, val, result, root.count + 1 + count)
            else:
                root.count += 1
                root.left = bst_insert(root.left, val, result, count)
            return root
 
        root = None
        result = []
        for num in reversed(nums):
            if not root:
                root = Node(num)
                result.append(0)
            else:
                bst_insert(root, num, result, 0)
        return result[::-1]

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