You're given an array of k linked lists, lists, each sorted in ascending order. Merge them all into one sorted linked list and return its head.
Lists are written as arrays: [[1, 4], [2]] means two lists, 1 → 4 and 2.
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
0 <= k <= 10^4- Each list has between
0and500nodes. -10^4 <= Node.val <= 10^4