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.

Input:

In this problem, method takes one argument: the head of the linked list. The function should not read any input from stdin/console.
The struct Node has a data part which stores the data and a next pointer which points to the next element of the linked list. 
There are multiple test cases. For each test case, this method will be called individually.

Output:
Pairwise swap linked list elements .

Note: If you use "Test" or "Expected Output Button" use below example format

Example:
Input:
1
8
1 2 2 4 5 6 7 8

Output:
2 1 4 2 6 5 8 7

** For More Input/Output Examples Use 'Expected Output' option **