# Reverse Alternative ‘k’ nodes in a Linked List.

**Objective**: Given a linked list and a number ‘k’, write an algorithm to reverse alternate ‘k’ nodes in the linked list.

This problem was asked in the Microsoft and Amazon interviews.

**Example**:

Recursion is the key here. Solution will be quite similar to “**Reverse a Linked List in groups of given siz****e ‘K’**” with some modifications. We can solve it in two methods-

- Taking ‘k’ nodes for a iteration.
- Taking ‘2k’ nodes for a iteration
**.**

**Method 1: Taking ‘k’ nodes for a iteration.**

- Take ‘k’ nodes at a time for one iteration and call rest of the recursively.
- In alternate iterations-
- Reverse the ‘k’ nodes.
- Skip the ‘k’ nodes.

- we use boolean variable to identify when to reverse OR Skip nodes.

**Method 2: Taking ‘2k’ nodes for a iteration. **

- Take 2’k’ nodes at a time for one iteration and call rest of the recursively.
- In every iteration-
- Reverse the first ‘k’ nodes.
- Skip the next ‘k’ nodes.

Look at the code for better understanding.

**Complete Code:**

**Output:**

Original Link List 1 : ->1->2->3->4->5->6->7->8->9->10->11->12 Recursion with 2k nodes where k = 2 ->2->1->3->4->6->5->7->8->10->9->11->12 Original Link List 2 : ->1->2->3->4->5->6->7->8->9->10->11->12 Recursion with k nodes where k=3 ->3->2->1->4->5->6->9->8->7->10->11->12