Reverse Linked List Problem Statement

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

Example:

Input:

The given linked list is 1 -> 2 -> 3 -> 4 -> NULL.

Output:

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

Explanation:

The original linked list is reversed so that the last element becomes the head.

Constraints:

• 1 <= T <= 5
• 0 <= L <= 10⁵
• 1 <= data <= 10⁹ and data != -1
• Time Limit: 1 sec

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.

Note:

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

Follow Up:

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