430 - Flatten A Multilevel Doubly Linked List
Written on January 7, 2020
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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.
class Solution:
def flatten(self, head: 'Node') -> 'Node':
if not head:
return head
dummy = Node(0, None, None, None)
dummy.next = head
while head:
if head.child:
child_head = self.flatten(head.child)
head.child = None
child_tail = self.get_tail(child_head)
head_next = head.next
head.next = child_head
child_head.prev = head
child_tail.next = head_next
if head_next:
head_next.prev = child_tail
head = head_next
else:
head = head.next
return dummy.next
def get_tail(self, node):
while node.next:
node = node.next
return node