"""
897. Increasing Order Search Tree
Easy

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]

 

Constraints:

    The number of nodes in the given tree will be in the range [1, 100].
    0 <= Node.val <= 1000
"""
# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def increasingBST(self, root: TreeNode) -> TreeNode:
        def dfs(node):
            b, e = node, node
            if node.left:
                lb, le = dfs(node.left)
                b = lb
                le.right = e
                e.left = None
            if node.right: 
                rb, re = dfs(node.right)
                e.right = rb
                e = re
            return b, e
        b, e = dfs(root)
        return b
