Sort a linked list in ascending order using constant space and O(n log n) time. Example: Input: head = [4,2,1,3] Output: [1,2,3,4] Explanation: The list is sorted via merge sort or similar. Pattern focus: Merge sort on linked lists (merging sorted sublists).
head = ListNode
return ListNode
Example 1:
Input:
head = [4,2,1,3]
Output:
[1,2,3,4]
Explanation:
Sorted ascending.