Posted: 27 Oct, 2020
Difficulty: Moderate

PROBLEM STATEMENT

Note:

The given linked lists may or may not be null.

For example:

If the first list is: 1 -> 4 -> 5 -> NULL and the second list is: 2 -> 3 -> 5 -> NULL

The final list would be: 1 -> 2 -> 3 -> 4 -> 5 -> 5 -> NULL
Input Format:
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 first line of each test case contains the elements of the first linked list separated by a single space and terminated by -1. Hence, -1 would never be a list element.

The second line of each test case contains the elements of the second linked list separated by a single space and terminated by -1.
Output Format:
For each test case, print the final linked list. The elements of the linked list must be separated by a single space and terminated by -1.

Print output of each test case in a separate line.
Note:
You are not required to print the expected output, it has already been taken care of. Just implement the function.
Constraints:
1 <= T <= 10
1 <= L <= 10^5
1 ≤ data ≤ 10^6 and data != -1

Where L is the number of nodes in either of the two Linked List.

Time Limit: 1 sec

Follow-up:

Try to solve this problem in linear time complexity and constant space complexity. Approach 1
• Without loss of generality, let’s say the head of the first linked list is smaller than the head of the second linked list.
• The current node would be the smaller of the two, i.e. the head of the first node, here.
• We run a recursive function, pointing to the next element of the head of the first linked list.
• If only one of the lists is empty, we return null.
• If both the lists are empty, we return null.