Grokking the Coding Interview: Patterns for Coding Questions
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Solution: Reverse every K-element Sub-list

Problem Statement

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

If, in the end, you are left with a sub-list with less than ‘k’ elements, reverse it too.

Constraints:

  • The number of nodes in the list is n.
  • 1 <= k <= n <= 5000
  • 0 <= Node.val <= 1000

Solution

The problem follows the In-place Reversal of a LinkedList pattern and is quite similar to Reverse a Sub-list. The only difference is that we have to reverse all the sub-lists. We can use the same approach, starting with the first sub-list (i.e.

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