Leetcode题目：python实现删除排序链表中的重复元素（遍历+循环)

思路：
遍历结点，遇到相同的跳过一个结点（删除）

    def deleteDuplicates(self, head):
        if head == None:
            return head
        cur = head
        while cur.next != None:
            first = cur.val
            ccur = cur.next
            second = ccur.val
            # 删除重复结点，保留其中一个
            if second == first:
                ccur = ccur.next
                cur.next = ccur
            else:
                cur = ccur
        return head

思路：
双指针：快慢指针，用快指针找到相同的或者不同的值，并用flag标记，找到不同的值后用慢指针指向。

    def deleteDuplicates(self, head: ListNode) -> ListNode:
        dummy = ListNode(0)
        slow = dummy
        fast = head
        while fast != None:
            # 是否快进的标志
            flag = False
            while fast.next !=None and fast.val == fast.next.val:
                flag = True
                fast = fast.next
            if not flag:
                slow.next = fast
                slow = slow.next
            fast = fast.next
        slow.next = None
        return dummy.next