Given the head of a linked list, return the list after sorting it in ascending order.
Follow up: Can you sort the linked list in O(n logn) time and O(1) memory (i.e. constant space)?
Input: head = [-1,5,3,4,0]
Output: [-1,0,3,4,5]
Input: head = [-1,5,3,4,0]
Output: [-1,0,3,4,5]
Input: head = []
Output: []
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