Merge K Sorted Lists

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Problem

Given an array of k linked lists, each sorted in ascending order, merge all of them into one sorted linked list and return its head.

Examples

Example 1

Input:lists = [[1,4,5],[1,3,4],[2,6]]

Output:[1,1,2,3,4,4,5,6]

Example 2

Input:lists = []

Output:[]

Constraints

0 <= k <= 10^4

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How to approach it: the Linked List pattern

A chain of nodes, each pointing to the next. No random access like an array, but insertion and deletion at a known position is O(1), and many classic problems come down to careful pointer rewiring.

Look for this pattern when

The problem explicitly gives you a linked list (reverse it, merge lists, detect a cycle, reorder it).
You need O(1) insertion/deletion without shifting elements, unlike an array.

Read the full Linked List guide →

Video walkthroughs

Original problem on LeetCode ↗