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 1: Input: head = [1,2,3,4,5,6,null,null,null,7,8,9,10,null,null,11,12] Output: [1,2,3,7,8,11,12,9,10,4,5,6] Explanation: The multilevel linked list in the input is as follows: After flattening the multilevel linked list it becomes:
- code
class Solution:
def flatten(self, head: 'Node') -> 'Node':
ans = head
def addChild(has_child_node):
later = has_child_node.next
child = has_child_node.child
has_child_node.next = child
child.prev = has_child_node
has_child_node.child = None
while child.next:
child = child.next
child.next = later
if later:
later.prev = child
while head:
if head.child:
addChild(head)
head = head.next
return ans