107. Merge K Sorted Lists

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Input: lists = [[1,4,5],[1,3,4],[2,6]]

Output: [1,1,2,3,4,4,5,6]

Explanation: The linked lists [1->4->5], [1->3->4], and [2->6] are merged into the sorted linked list 1->1->2->3->4->4->5->6.

Input: lists = []

Output: null

Explanation: An empty list of lists results in an empty merged list.

Input: lists = [[]]

Output: null

Explanation: A list containing only an empty list results in an empty merged list.

Time Complexity

O(N log k)

Space Complexity

O(k)