数组 26、27、80

快慢指针，
fast指向当前处理的值
slow的值代表：遇到合法的值，将合法的值放在slow的位置。

• lc80

def removeDuplicates(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        if len(nums) <= 2:
            return len(nums)
        slow = 2
        for fast in range(2, len(nums)):
            if (nums[fast] == nums[slow-1]) and (nums[slow-1] == nums[slow-2]):
                continue
            else:
                nums[slow] = nums[fast]
                slow += 1
        return slow