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.

Solution

class Solution:
    def increasingBST(self, root: TreeNode) -> TreeNode:
        f = self.reverse_flatten(root)

        root = None
        for num in f:
            root = TreeNode(num, None, root)

        return root

    def reverse_flatten(self, root: Optional[TreeNode]) -> List[int]:
        if root is None:
            return []

        return (
            self.reverse_flatten(root.right)
            + [root.val]
            + self.reverse_flatten(root.left)
        )


class TreeNode:
    def __init__(self, val=0, left=None, right=None):
        self.val = val
        self.left = left
        self.right = right