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**. Since it is impossible to change the length of the array in some languages, you must instead have the result be placed in the **first part** of the array `nums`. More formally, if there are `k` elements after removing the duplicates, then the first `k` elements of `nums` should hold the final result. It does not matter what you leave beyond the first `k` elements. Return `k`_ after placing the final result in the first _`k`_ slots of _`nums`. Do **not** allocate extra space for another array. You must do this by **modifying the input array in-place** with O(1) extra memory. **Custom Judge:** The judge will test your solution with the following code: int[] nums = [...]; // Input array int[] expectedNums = [...]; // The expected answer with correct length int k = removeDuplicates(nums); // Calls your implementation assert k == expectedNums.length; for (int i = 0; i < k; i++) { assert nums[i] == expectedNums[i]; } ``` If all assertions pass, then your solution will be **accepted**.   **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 * 104` - `-104 <= nums[i] <= 104` - `nums` is sorted in **non-decreasing** order.