Remove Duplicates from Sorted List II

Given the head of a sorted linked list, delete all nodes that have duplicate numbers, leaving only distinct numbers from the original list. Return the linked list sorted as well.

Example 1:

Input: head = [1,2,3,3,4,4,5]
Output: [1,2,5]

Example 2:

Input: head = [1,1,1,2,3]
Output: [2,3]

Constraints:

• The number of nodes in the list is in the range [0, 300].
• -100 <= Node.val <= 100
• The list is guaranteed to be sorted in ascending order.

SOLUTION:

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
    def deldup(self, head: Optional[ListNode]) -> Optional[ListNode]:
        if not head:
            return head
        if head.val in self.dups or (head.next and head.val == head.next.val):
            self.dups.add(head.val)
            head = self.deldup(head.next)
        else:
            head.next = self.deldup(head.next)
        return head

    def deleteDuplicates(self, head: Optional[ListNode]) -> Optional[ListNode]:
        self.dups = set()
        head = self.deldup(head)
        return head