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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 k2 times, since we need one pointer each at both ends for swapping so move pointers only k2 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);
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
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