80. Remove Duplicates from Sorted Array II

Given an integer array nums sorted in non-decreasing order, remove some duplicates in-place such that each unique element appears at most twice. The relative order of the elements should be kept the same

Example 1:

• Input: nums = [1,1,1,2,2,3]
• Output: 5, nums = [1,1,2,2,3,_]
• Explanation: Your function should return k = 5, with the first five elements of nums being 1, 1, 2, 2 and 3 respectively. It does not matter what you leave beyond the returned k (hence they are underscores).

Example 2:

• Input: nums = [0,0,1,1,1,1,2,3,3]
• Output: 7, nums = [0,0,1,1,2,3,3,_,_]
• Explanation: Your function should return k = 7, with the first seven elements of nums being 0, 0, 1, 1, 2, 3 and 3 respectively. It does not matter what you leave beyond the returned k (hence they are underscores).

Constraints:

• 1 <= nums.length <= 3 * 10^4
• -10^4 <= nums[i] <= 10^4
• nums is sorted in non-decreasing order.

Solution

class Solution:
    def removeDuplicates(self, nums: list[int]) -> int:
        slow = 0
        for fast in range(len(nums)):
            if slow < 2 or nums[fast] != nums[slow - 2]:
                nums[slow] = nums[fast]
                slow += 1
        return slow