# 114 二叉树展开为链表

给定一个二叉树，原地将它展开为链表。

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

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

            if root.left:
                left_ptr = root.left
                while (left_ptr.right):
                    left_ptr = left_ptr.right
                left_ptr.right = root.right
                root.right = root.left
                root.left = None