Reverse the Linked List

Given a singly linked list of integers, your task is to return the head of the reversed linked list.

Input:

The first line of input contains an integer 'T' representing the number of test cases or queries to be processed. Then the test case follows.

The only line of each test case contains the elements of the singly linked list separated by a single space and terminated by -1. Hence, -1 would never be a list element.

Output:

For each test case, print the given linked list in reverse order in a separate line.

Example:

Given the linked list: 1 -> 2 -> 3 -> 4 -> NULL
The reversed linked list is: 4 -> 3 -> 2 -> 1 -> NULL
The head of the reverse linked list will be 4.

Constraints:

• 1 <= T <= 5
• 0 <= L <= 10^5
• 1 <= data <= 10^9 and data != -1

Note:

You do not need to print anything; it has already been taken care of. Just implement the given function.

Additional Information:

Can you solve this problem in O(N) time and O(1) space complexity?