Good morning! Here's our prompt for today.

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:

1function Node(val) {
2  this.value = val;
3  this.next = null;
4}

Here's how it would be invoked:

1// Input
2const arr = [
3  2 -> 6 -> 9,
4  1 -> 2 -> 7,
5  2 -> 6 -> 10
6]
7
8mergeLists(arr);
9
10// Output
111 -> 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)

Try to solve this here or in Interactive Mode.

How do I practice this challenge?

xxxxxxxxxx

    'PASSED: Expect `mergeLists(2 -> 6 -> 9, 1 -> 2 -> 7, 2 -> 6 -> 10)` to return 1 -> 2 -> 2 -> 2 -> 6 -> 6 -> 7 -> 9 -> 10'

var assert = require('assert');

​

function mergeLists(arrOfLists) {

  // fill in this method

  return [];

}

​

// Supporting data structures

​

function Node(val) {

  this.val = val;

  this.next = null;

}

​

class LinkedList {

  constructor() {

    this.head = null;

    this.tail = null;

  }

​

  prepend(newVal) {

    const currentHead = this.head;

    const newNode = new Node(newVal);

    newNode.next = currentHead;

    this.head = newNode;

​

    if (!this.tail) {

      this.tail = newNode;

    }

Here's a video of us explaining the solution.

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We'll now take you through what you need to know.

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