[Leetcode] Remove Duplicates from Sorted List II

Intuition

My first approach to this problem is that call method recursively and find out the next head (not duplicated)
I assume that there are two possible cases

My Approach

if duplicated value exist next to current node

• current node should change to another node which value is not same with current node
• then return current node

if duplicated value doesn`t exist next to current node

• return current node

class Solution:
    def deleteDuplicates(self, head: Optional[ListNode]) -> Optional[ListNode]:
        if head == None or head.next == None:
            return head
        # Define left, right point

        print(head.val, head.next.val)

        if head.val == head.next.val:
            temp = self.deleteDuplicates(head.next)
            if temp == None:
                return temp
            if temp.val == head.val:
                return temp.next
            return temp

        head.next = self.deleteDuplicates(head.next)
        return head

Other Solution

Other ways two solve this problem is to use Sentinal Node
Their primary purpose is to standardize the situation to avoid edge case handling