114.Flatten-Binary-Tree-to-Linked-List.py

# https://leetcode.com/problems/flatten-binary-tree-to-linked-list/
#
# algorithms
# Medium (43.7%)
# Total Accepted:    256,628
# Total Submissions: 587,307


# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
    def flatten(self, root):
        """
        :type root: TreeNode
        :rtype: None Do not return anything, modify root in-place instead.
        """
        if not root:
            return None

        res = root

        while root:
            if root.left:
                pre = root.left
                while pre.right:
                    pre = pre.right
                pre.right = root.right
                root.right = root.left
                root.left = None

            root = root.right

        return res