Grokking Data Structures & Algorithms for Coding Interviews
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Solution: Reorder List

Problem Statement

Reorder a singly linked list so the nodes come in the order first, last, second, second to last, and so on, changing only the links. Return the head.

Examples

Example 1

  • Input: head = [1, 2, 3, 4]
  • Expected Output: [1, 4, 2, 3]

Example 2

  • Input: head = [1, 2, 3, 4, 5]
  • Expected Output: [1, 5, 2, 4, 3]

Example 3

  • Input: head = [1, 2]
  • Expected Output: [1, 2]

What makes this hard

The required order needs the last node early, and a singly linked list gives you no way back

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