打卡群刷题总结0813——二叉树展开为链表

# Definition for a binary tree node.# class TreeNode(object):#     def __init__(self, val=0, left=None, right=None):#         self.val = val#         self.left = left#         self.right = rightclass Solution(object):    def traverse(self, node, parent):        parent.right = node        last_node = node        right = node.right        if node.left:            last_node = self.traverse(node.left, last_node)            node.left = None        if right:            last_node = self.traverse(right, last_node)        return last_node        def flatten(self, root):        """        :type root: TreeNode        :rtype: None Do not return anything, modify root in-place instead.        """        if not root:            return root        parent = ListNode(0)        self.traverse(root, parent)        return parent.right