Reverse Linked List Problem Statement

Given a singly linked list of integers, return the head of the reversed linked list.

Example:

Initial linked list: 1 -> 2 -> 3 -> 4 -> NULL
Reversed linked list: 4 -> 3 -> 2 -> 1 -> NULL
The head of the reversed linked list is 4.

Follow Up:

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

Input:

The first line contains an integer 'T' representing the number of test cases.
Each test case consists of a single line containing the elements of the singly linked list, separated by a space and terminated with -1 (indicating the end of the list). The value -1 is not part of the list.

Output:

For each test case, print the reversed linked list in a separate line.

Constraints:

• 1 <= T <= 5
• 0 <= L <= 10^5
• 1 <= data <= 10^9 and data ≠ -1
• Time Limit: 1 sec

Note:

You do not need to print anything; implement the function provided.