Leetcode 766 Solution

This article provides solution to leetcode question 766 (flatten-a-multilevel-doubly-linked-list)
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https://leetcode.com/problems/flatten-a-multilevel-doubly-linked-list

Solution

"""
# 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
"""
class Solution:
    def flatten(self, head):
        if not head:
            return None

        s = []
        s.append(head)
        prev = None

        while s:
            node = s.pop(-1)

            if node.next:
                s.append(node.next)
            if node.child:
                s.append(node.child)

            node.prev = prev
            if prev:
                prev.next = node
            node.child = None
            node.next = None

            prev = node

        return head