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Merge K Sorted Lists

Explore how to merge k sorted singly linked lists into a single sorted list using k-way merge techniques. Understand the problem constraints and develop a solution that efficiently combines multiple sorted lists. This lesson equips you with the skills to handle linked list merging challenges common in coding interviews.

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Statement

You are given an array, lists, containing k singly linked lists. Each of these linked lists is individually sorted in ascending order.

Your task is to merge all k linked lists into a single sorted linked list in ascending order and return the merged list.

Constraints:

  • k ==== lists.length

  • 0≤0 \leq k ≤103\leq 10^3

  • 0≤0 \leq lists[i].length ≤500\leq 500

  • −103≤-10^3 \leq lists[i][j] ≤103\leq 10^3

  • Each lists[i] is sorted in ascending order.

  • The sum of all lists[i].length will not exceed 10310^3.

Examples

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Understand the problem

Let’s take a moment to make sure you’ve correctly understood the problem. The quiz below helps you check if you’re solving the correct problem:

Merge K Sorted Lists

1.

What is the output if the following array is given as input?

lists = [
               1 → 2 → 3 → NULL,
               12 → 56 → 200 → NULL,
               -10 → -2 → 5 → NULL
            ]

A.

1 → 2 → 3 → 12 → 56 → 200 → -10 → -2 → 5 → NULL

B.

1 → 2 → 3 → -10 → -2 → 5 → 12 → 56 → 200 → NULL

C.

-10 → -2 → 1 → 2 → 3 → 5 → 12 → 56 → 200 → NULL

D.

-10 → -2 → 5 → 1 → 2 → 3 → 12 → 56 → 200 → NULL

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Figure it out!

We have a game for you to play. Rearrange the logical building blocks to develop a clearer understanding of how to solve this problem.

Sequence - Vertical
Drag and drop the cards to rearrange them in the correct sequence.
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Try it yourself

Implement your solution in the following coding playground.

Java
usercode > Solution.java
// Definition for a Linked List node
// class ListNode {
//     int val;
//     ListNode next;
//     // Constructor
//     public ListNode(int val) {
//         this.val = val;
//         this.next = null;
//     }
// }
import ds_v1.LinkedList.ListNode;
import java.util.*;
class Solution {
	public static ListNode mergeKLists(ListNode[] lists) {
        
		// Replace this placeholder return statement with your code
		return null;
	}
}
Merge K Sorted Lists