You are given an array, lists, containing k singly linked lists. Each of these linked lists is individually sorted in ascending order.

Your task is to merge all k linked lists into a single sorted linked list in ascending order and return the merged list.

Constraints:

• k $==$ lists.length

• $0 \leq$ k $\leq 10^3$

• $0 \leq$ lists[i].length $\leq 500$

• $-10^3 \leq$ lists[i][j] $\leq 10^3$

• Each lists[i] is sorted in ascending order.

• The sum of all lists[i].length will not exceed $10^3$.