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

Question

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?

Accepted Answer

Reverse a singly linked list of integers in O(N) time and O(1) space complexity.

Iterate through the linked list, reversing the pointers to point to the previous node instead of the next node.
Use three pointers to keep track of the current, previous, and next nodes while reversing the list.
Update the head of the reversed linked list as the last node encountered during the reversal process.
Example: Given 1 -> 2 -> 3 -> 4 -> NULL, reverse it to get 4 -> 3 -> 2 -> 1 -> NULL with head as 4.

Reverse the Linked List

Input:

Output:

Example:

Constraints:

Note:

Additional Information:

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