[Leet Code] Increasing Order

Leetcode: https://leetcode.com/problems/increasing-order-search-tree/

Problem:

Given the root of a binary search tree, rearrange the tree in in-order so that the leftmost node in the tree is now the root of the tree, and every node has no left child and only one right child.

Example 1:

Input: root = [5,3,6,2,4,null,8,1,null,null,null,7,9]
Output: [1,null,2,null,3,null,4,null,5,null,6,null,7,null,8,null,9]

Example 2:

Input: root = [5,1,7]
Output: [1,null,5,null,7]

Solution:

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution(object):
    def increasingBST(self, root):
        """
        :type root: TreeNode
        :rtype: TreeNode
        """
        if root and root.left or root.right:
            elements = []
            self.inorder(root, elements)
            answers = []
            for i in range(0,len(elements)-1):
                node = elements[i]
                node.right = elements[i+1]
                answers.append(node)
            return answers[0]
        else:
            return root
                
    def inorder(self, root, elements):
        if root:
            self.inorder(root.left, elements)
            node = TreeNode()
            node.val = root.val
            elements.append(node)
            self.inorder(root.right, elements)