114. Flatten Binary Tree to Link

相当于吧rightMovingChunk的root端一点点增加上去

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

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