# # 【LeetCode】430. Flatten a Multilevel Doubly Linked List 解题报告（Python）

## # 题目描述：

You are given a doubly linked list which in addition to the next and previous pointers, it could have a child pointer, which may or may not point to a separate doubly linked list. These child lists may have one or more children of their own, and so on, to produce a multilevel data structure, as shown in the example below.

Flatten the list so that all the nodes appear in a single-level, doubly linked list. You are given the head of the first level of the list.

Example:

``````Input:
1---2---3---4---5---6--NULL
|
7---8---9---10--NULL
|
11--12--NULL

Output:
1-2-3-7-8-11-12-9-10-4-5-6-NULL
``````

Explanation for the above example:

Given the following multilevel doubly linked list:

We should return the following flattened doubly linked list:

## # 解题方法

``````"""
# Definition for a Node.
class Node(object):
def __init__(self, val, prev, next, child):
self.val = val
self.prev = prev
self.next = next
self.child = child
"""
class Solution(object):
"""
:rtype: Node
"""
while node:
node_next = node.next
if node.child:
flattened = self.flatten(node.child)
node.child = None
nextNode = self.appendToList(node, flattened)
node = nextNode
else:
node = node.next

next_node = node.next