C# || How To Flatten A Multilevel Doubly Linked List Using C#

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The following is a module with functions which demonstrates how to flatten a doubly linked list using C#.

1. Flatten – Problem Statement

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]

The multilevel linked list in the input is as follows:

Example 1

After flattening the multilevel linked list it becomes:

Example 1

Example 2:

Input: head = [1,2,null,3]
Output: [1,3,2]

The input multilevel linked list is as follows:


Example 3:

Input: head = []
Output: []

2. Flatten – Solution

The following are two solutions which demonstrates how to flatten a doubly linked list.



The highlighted lines are sections of interest to look out for.

The code is heavily commented, so no further insight is necessary. If you have any questions, feel free to leave a comment below.

Once compiled, you should get this as your output for the example cases:


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