Merge K Sorted Lists

You are given an array of k linked lists, each sorted in ascending order. Merge all the linked lists into one sorted linked list and return it.

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Example 1

lists[0]: 1 -> 4 -> 5
lists[1]: 1 -> 3 -> 4
lists[2]: 2 -> 6

Input: lists = [[1,4,5],[1,3,4],[2,6]]
Output: [1,1,2,3,4,4,5,6]
Explanation: Merging the three sorted lists produces one sorted list with all elements.

Example 2

Input: lists = []
Output: []
Explanation: No lists to merge, so the result is empty.

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Constraints

• k == lists.length
• 0 <= k <= 10^4
• 0 <= lists[i].length <= 500
• -10^4 <= lists[i][j] <= 10^4
• lists[i] is sorted in ascending order.
• The sum of all lists[i].length will not exceed 10^4.