Merge K Sorted Lists

Problem

Merge k sorted linked lists into one sorted list.

Input / Output

• Input: an array of k sorted linked-list heads.
• Output: the head of a single merged, sorted linked list.

Constraints

• 0 ≤ k ≤ 10^4

Example

[[1,4,5],[1,3,4],[2,6]] -> [1,1,2,3,4,4,5,6]