Remove duplicates from singly link list.

Write code to remove duplicates from an unsorted linked list.

Approach:
Create a hashtable.
Iterate through the list and check the node if its already present in the hashtable, if present then delete it from the list.
If not then add it to the hashtable and move ahead in the list.


Input/Output:
Original linked list:
2 -> 3 -> 2 -> 5 -> 2 -> 8 -> 2 -> 3 -> 8 -> null
After deleting duplicate node:
2 -> 3 -> 5 -> 8 -> null

Time complexity: O(n) -> n is the length of the linked list.
Space complexity: O(n) -> size of the hashtable.