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Problem Challenge 1: Reverse alternating K-element Sub-list (medium)

Problem Statement

Given the head of a LinkedList and a number k, reverse every alternating k sized sub-list starting from the head.

The first k nodes are reversed, the next k are left alone, the next k are reversed, and so on. If the last group holds fewer than k nodes, treat it the same way as a full group: reverse it if it falls on a reversing turn, leave it alone if it falls on a skipping turn.

Example:

Input:  1 -> 2 -> 3 -> 4 -> 5 -> 6 -> 7 -> 8 -> 9 -> 10 -> null,  k = 3
Output: 3 -> 2 -> 1 -> 4 -> 5 -> 6 -> 9 -> 8 -> 7 -> 10 -> null

Nodes 1 to 3 are reversed, 4 to 6 are skipped, 7 to 9 are reversed, and the final group holds only node 10. That group falls on a skipping turn, so it stays where it is.

Image

Constraints:

  • The number of nodes in the list is n.
  • 1 <= n <= 5000
  • 1 <= k <= 5000 (k may be larger than n)
  • 0 <= Node.val <= 1000

Try it yourself

Try solving this question here:

Python3
Python3
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