Source: https://www.algoexpert.io/questions/remove-duplicates-from-linked-list
Difficulty: easy
Category: Linked Lists
You're given the head of a Singly Linked List whose nodes are in sorted order with respect to their values. Write a function that returns a modified version of the Linked List that doesn't contain any nodes with duplicate values. The Linked List should be modified in place (i.e., you shouldn't create a brand new list), and the modified Linked List should still have its nodes sorted with respect to their values.
Each LinkedList node has an integer value as well as a next node pointing
to the next node in the list or to None / null if it's the tail of the list.
Sample Input
linkedList = 1 -> 1 -> 3 -> 4 -> 4 -> 4 -> 5 -> 6 -> 6 // the head node with value 1
Sample Output
1 -> 3 -> 4 -> 5 -> 6 // the head node with value 1