Here is the interview question prompt, presented for reference.

You're given an array of multiple sorted linked lists. Can you write a method that returns it transformed into a single sorted linked list?

Each linked list can be represented as a series of nodes with the following definition:

function Node(val) {
  this.value = val;
  this.next = null;
}

Here's how it would be invoked:

// Input
const arr = [
  2 -> 6 -> 9,
  1 -> 2 -> 7,
  2 -> 6 -> 10
]

mergeLists(arr);

// Output
1 -> 2 -> 2 -> 2 -> 6 -> 6 -> 7 -> 9 -> 10

Constraints

• Each list can have up to 100000 nodes
• The cumulative sum of all the nodes in the linked lists will be <= 100000
• The values in the nodes will be in the range -1000000000 and 1000000000
• Let n and k be the length of a linked list and number of lists
• Expected time complexity : O(n*k*log k)
• Expected space complexity : O(k)

You can see the full challenge with visuals at this link.