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.length0 <= k <= 10^40 <= lists[i].length <= 500-10^4 <= lists[i][j] <= 10^4lists[i] is sorted in ascending order.lists[i].length won't exceed 10^4.