Merge k Sorted Lists
Difficulty: Hard
Category: DSA
Topics: Linked List, Divide and Conquer, Heap (Priority Queue), Merge Sort
Asked at: Amazon, Facebook, Microsoft, Bloomberg, Apple, Oracle, Databricks, Google, Twitter, Uber, Adobe, Wish, ByteDance, Palantir Technologies, Tesla
You are given an array of `k` linked-lists `lists`, each linked-list is sorted in ascending order.
_Merge all the linked-lists into one sorted linked-list and return it._
**Example 1:**
**Input:** lists = [[1,4,5],[1,3,4],[2,6]]
**Output:** [1,1,2,3,4,4,5,6]
**Explanation:** The linked-lists are:
[
1->4->5,
1->3->4,
2->6
]
merging them into one sorted list:
1->1->2->3->4->4->5->6
```
**Example 2:**
**Input:** lists = []
**Output:** []
```
**Example 3:**
**Input:** lists = [[]]
**Output:** []
```
**Constraints:**
- `k == lists.length`
- `0 <= k <= 104`
- `0 <= lists[i].length <= 500`
- `-104 <= lists[i][j] <= 104`
- `lists[i]` is sorted in **ascending order**.
- The sum of `lists[i].length` will not exceed `104`.