Grokking the Coding Interview: Patterns for Coding Questions
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Solution: Problem Challenge 1: Reverse alternating K-element Sub-list

Problem Statement

Given the head of a LinkedList and a number ‘k’, reverse every alternating ‘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 every K-element Sub-list. The only difference is that we have to skip ‘k’ alternating elements

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Lucas

· 4 years ago

Here is my solution! Hope it doesnt crack under pressure :) Image

Shaho Shahbazpanahi

Shaho Shahbazpanahi

· a year ago

For this input [1,2,3,4,5,6,7,8,9,10,11] and k= 3, then expected output should be [3,2,1,6, 5, 4,10, 8,9,11, 10] while the solution give us [3,2,1,6, 5, 4,10, 8,9, 10, 11] , the problem stats if the rest of lis is smaller than k, revese it to .