Merge K Sorted Arrays

You're given lists, a list of k lists, each sorted in ascending order. Merge them into one sorted list and return it.

(LeetCode 23 asks the same with linked lists; the heap idea is identical.)

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: []

Example 3

Input: lists = [[]]
Output: []

Constraints

• 0 <= k <= 10^4
• 0 <= len(lists[i]) <= 500
• Total number of values N <= 10^5
• Each lists[i] is sorted ascending