Leetcode 82. Remove Duplicates from Sorted List II

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution:
    def deleteDuplicates(self, head: ListNode) -> ListNode:
        dummyHead = dummy = ListNode(0)
        dummy.next = head

        dupFlag = False
        
        while head is not None and head.next is not None:
            # Find duplicated elements.
            if head.val == head.next.val :
                # Delete duplicated elements one by one.
                while head.next is not None and head.next.val == head.val :
                    head = head.next
                
                # Delete last duplicated element.
                head = head.next
                dummy.next = head
            else :
                # Skip different elements.
                dummy = dummy.next
                head = head.next
        
        return dummyHead.next