merge-k-sorted-lists code addition

[harrdy272]

Pull Request Template

Description

Problem states that we have to merge k number of linked lists which are in sorted order and we have to make the resultant linked list also in sorted order. I have used multiset and made a function to insert nodes at the end of linked list, which helped me to make a new linked list in sorted format very easily.

Put check marks:

Have you made changes in README file ?

• Added problem & solution under correct topic.
• Specified Space & Time complexity.
• Specified difficulty level, tag & Note(if any).

How Has This Been Tested?

Tests have been made and the code is working fine. Following are some sample test cases:

• lists = [[1,4,5],[1,3,4],[2,6]]
• lists = [[]]

Make sure all below guidelines are followed else PR will get Reject:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code so that it is easy to understand
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules