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Merge k Sorted Lists

hard

You are given an array of k linked-lists lists, each linked-list is sorted in ascending order.

Merge all the linked-lists into one sorted linked-list and return it.

Examples

Example 1

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

Example 2

Input:  lists = []
Output: []

Example 3

Input:  lists = [[]]
Output: []

Constraints

  • k == lists.length
  • 0 <= k <= 10000
  • 0 <= lists[i].length <= 500
  • -10000 <= lists[i][j] <= 10000
  • lists[i] is sorted in ascending order

How the tests work: each list is written as an array — [1,4,5] is 1 → 4 → 5 — and your function receives their ListNode heads. The merged list is read back into an array.

TypeScript
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List of test cases (10)
Case 1
lists = [[1,4,5],[1,3,4],[2,6]]
Case 2
lists = []
Case 3
lists = [[]]
Case 4
lists = [[1]]
Case 5
lists = [[1,2,3],[4,5,6]]
Case 6
lists = [[5],[3],[1],[4],[2]]
Case 7
lists = [[-1,0,1],[-2,2],[-3,3]]
Case 8
lists = [[1,1,1],[1,1,1]]
Case 9
lists = [[],[1],[]]
Case 10
lists = [[1,3,5,7],[2,4,6,8],[0,9,10]]