83. Remove Duplicates from Sorted List

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
    def deleteDuplicates(self, head: Optional[ListNode]) -> Optional[ListNode]:
        if not head or not head.next:        # one or less nodes
            return head

        prev = head
        current = head

        while current and current.next:
            current = current.next
            if prev.val == current.val:
                prev.next = current.next

            else:
                prev = prev.next


        return head