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);
Complete 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