Given an array of linked lists, each sorted in ascending order, merge all lists into one sorted list and return it.
Example: For [[1,4,5],[1,3,4],[2,6]], return [1,1,2,3,4,4,5,6].
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Given an array of linked lists, each sorted in ascending order, merge all lists into one sorted list and return it.
Example: For [[1,4,5],[1,3,4],[2,6]], return [1,1,2,3,4,4,5,6].