Swap Nodes in Pairs

Given a linked list, swap every two adjacent nodes and return its head.

You must solve the problem without modifying the values in the list’s nodes (i.e., only nodes themselves may be changed.)

Class Node:
    data (int)
    next (Node)

Input Format

First Parameter - Node head

Output Format

Return the Node

Example 1 :

Input:
    LinkedList :  1 2 2 4 5 6 7 8
Output: 
    2 1 4 2 6 5 8 7
Explanation: 
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 a new linked list.

Example 2:

Input:
    LinkedList :  1 3 4 7 9 10 1
Output: 
    3 1 7 4 10 9 1
Explanation: After swapping each pair considering (1,3), (4, 7), (9, 10).. so
on as pairs, we get 3, 1, 7, 4, 10, 9, 1 as a new linked list.

Constraints:

• 1 ≤ N ≤ 10³
• 0 <= Node.data <= 100
• Expected Time Complexity: O(N).
• Expected Auxiliary Space: O(1).