Swap Every Kth Node in a LinkedList

Objective: Given a linked list, swap every kth node in that. If at the end of the list remaining nodes are less than k, leave them untouched.

Input: A linked list, A number k.

Example:

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

Approach:

  • Take 3 Pointers, ptrOne, ptrTwo and ptrTwo_prev.
  • ptrOne and ptrTwo_prev points at head node.
  • ptrTwo points at next node of ptrTwo_prev.
  • Move the ptrTwo and ptrTwo_prev k-2 times, since we need one pointer each at both ends for swapping so move pointers only k-2 times.
  • Create another pointer , NewHead and point it to ptrTwo.next.
  • Now we have ptrOne at head and ptrTwo at kth position, swap them with the help of ptrTwo_prev.
  • This function will returns the head.
  • Now make a recursive call with newHead.

ptrOne.next = reverseNodes(newHead, k);

Swap Evey Kth Node in a linked list
Swap Evey Kth Node in a linked list

Code:

Output:

Original Link List 1 : ->1->2->3->4->5->6->7->8->9->10
Swap Every 4th Node :
->4->2->3->1->8->6->7->5->9->10