82. Remove Duplicates from Sorted List II

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# 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]:
        dummy=ListNode(-200,head)
        prev=dummy
        curr=dummy
        flag=False

        cnt=0
        while curr:
            # print(curr.val)
            if curr.next==None:
                if flag:
                    prev.next=None
                # else:
                #     prev.next=curr
                break
            else:
                if curr.val==curr.next.val:
                    flag=True
                else:
                    
                    if flag==False:
                    #     prev.next=curr
                        prev=curr
                    if flag==True:
                        flag=False
                        prev.next=curr.next
                
                curr=curr.next
            # cnt+=1
            # if cnt>5:
            #     return   
        return dummy.next
        

考虑不同情况