Grokking the Coding Interview: Patterns for Coding Questions
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Problem Challenge 2: Rearrange a LinkedList (medium)

Problem Statement

Given the head of a Singly LinkedList, write a method to modify the LinkedList such that the nodes from the second half of the LinkedList are inserted alternately to the nodes from the first half in reverse order. So if the LinkedList has nodes 1 -> 2 -> 3 -> 4 -> 5 -> 6 -> null, your method should return 1 -> 6 -> 2 -> 5 -> 3 -> 4 -> null.

Your algorithm should use only constant space the input LinkedList should be modified in-place.

Example 1:

Input: 2 -> 4 -> 6 -> 8 -> 10 -> 12 -> null
Output: 2 -> 12 -> 4 -> 10 -> 6 -> 8 -> null

Example 2:

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