【LeetCode】 82.删除排序链表中的重复元素II

1. 题目

2. 分析

可以人为插入一个点，用于简化分析。

3. 代码

# 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]:
        start = ListNode(val=-1,next=None) # 新建一个头节点
        pre = start
        flag = 0
        while(head and head.next):
            if ( head.next and head.val != head.next.val):
                pre.next = head
                pre = head
                head = head.next # 往下走一个
                pre.next = None
            while(head.next and head.val == head.next.val):
                head = head.next
                flag = 1
            if flag:
                head = head.next # 还得再往下走            
                flag = 0
        if head:
            pre.next = head
        return start.next