Merge Two Sorted Linked Lists

Moderate

0/80

Average time to solve is 15m

299 upvotes

Asked in companies

Problem statement

You are given two sorted linked lists. You have to merge them to produce a combined sorted linked list. You need to return the head of the final linked list.

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

Detailed explanation ( Input/output format, Notes, Images )

Input Format:

The first line of input 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 input contains the elements of the second linked list separated by a single space and terminated by -1.

Output Format:

Print the final linked list. The elements of the linked list must be separated by a single space and terminated by -1.

Note:

You are not required to print the expected output, it has already been taken care of. Just implement the function.

Constraints:

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.

Sample Input 1:

7 8 -1
1 3 4 6 -1

Sample Output 1:

1 3 4 6 7 8 -1

Explanation of Input 1:

In this testcase, the first list is: 7 -> 8 -> NULL
The second list is: 1 -> 3 -> 4 -> 6 -> NULL
The final list would be: 1 -> 3 -> 4 -> 6 -> 7 -> 8 -> NULL

Sample Input 2:

5 -1
1 3 6 10 -1

Sample Output 2

1 3 5 6 10 -1

Console