LeetCode - 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.

 

My Solution:

# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution(object):
    def deleteDuplicates(self, head):
        """
        :type head: Optional[ListNode]
        :rtype: Optional[ListNode]
        """
        
        if head is None:
            return None
        if head.next is None:
            return head
        
        dummy = ListNode()
        dummy.next = head
        prev = dummy

        dup_vals = set()
        node = head
        while node:
            next_node = node.next

            if (node.next and node.val == node.next.val) or node.val in dup_vals:
                dup_vals.add(node.val)
                del_node = node
                prev.next = del_node.next
                del_node.next = None
                print(del_node)
                del del_node
            else:
                prev = node
            
            node = next_node
        
        return dummy.next