Given a singly linked list of size N. The task is to swap elements pairwise.

Input:
First line of input contains number of testcases T. For each testcase, first line of input contains length of linked list and next line contains linked list data.

Output:
Output the linked list after swapping pairwise nodes.

User Task:
The task is to complete the function pairWiseSwap() which takes head reference as the only argument and returns nothing.

Constraints:
1 <= T <= 100
1 <= N <= 10³

Example:
Input:
1
8
1 2 2 4 5 6 7 8

Output:
2 1 4 2 6 5 8 7

Explanation:
Testcase 1: After swapping each pair considering (1,2), (2, 4), (5, 6).. so on as pairs, we get 2, 1, 4, 2, 6, 5, 8, 7 as new linked list.
 

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