# Pairwise swap elements of a given linked list

Given a singly linked list, write a function to swap elements pairwise. For example, if the linked list is 1->2->3->4->5 then the function should change it to 2->1->4->3->5, and if the linked list is 1->2->3->4->5->6 then the function should change it to 2->1->4->3->6->5.

METHOD 1 (Iterative)
Start from the head node and traverse the list. While traversing swap data of each node with its next node’s data.

## C#

Output:

1 2 3 4 5
2 1 4 3 5

Time complexity: O(n)

METHOD 2 (Recursive)
If there are 2 or more than 2 nodes in Linked List then swap the first two nodes and recursively call for rest of the list.

 /* Recursive function to pairwise swap elements of a linked list */ void pairWiseSwap(struct node *head) {   /* There must be at-least two nodes in the list */   if (head != NULL && head->next != NULL)   {       /* Swap the node's data with data of next node */       swap(&head->data, &head->next->data);             /* Call pairWiseSwap() for rest of the list */       pairWiseSwap(head->next->next);   }   }

Time complexity: O(n)

The solution provided there swaps data of nodes. If data contains many fields, there will be many swap operations. See this for an implementation that changes links rather than swapping data.

Please write comments if you find any bug in above code/algorithm, or find other ways to solve the same problem.