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187. 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:
Approach:
Recursion is the key here. Solution will be quite similar to "Reverse a Linked List in groups of given size '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.
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