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 <= 1040 <= lists[i].length <= 500-104 <= lists[i][j] <= 104lists[i] is sorted in ascending order.lists[i].length will not exceed 104.