class Solution:
    def removeDuplicates(self, nums: List[int]) -> int:
        if not nums:
            return 0
        nums_length = len(nums)
        fast = slow = 1
        while fast < nums_length :
            if nums[fast] != nums[fast-1] :
                nums[slow] = nums[fast]
                slow += 1
            fast += 1
        return slow