60_Flatten_a_Multilevel_Doubly_Linked_List

"""
# Definition for a Node.
class Node:
    def __init__(self, val, prev, next, child):
        self.val = val
        self.prev = prev
        self.next = next
        self.child = child
"""
def solve(head):
    ptr=head
    temp=None
    prev=None
    while ptr:
        if ptr.child:
            temp=ptr.next
            ptr.next=ptr.child
            ptr.next.prev=ptr
            ptr.child=None
            temp1=solve(ptr.next)
            if temp1:
                temp1.next=temp
            if temp:
                temp.prev=temp1
        prev=ptr
        ptr=ptr.next
        
    return prev
class Solution:
    def flatten(self, head: 'Optional[Node]') -> 'Optional[Node]':
        temp=solve(head)
        return head