class Solution {
public:
    int removeDuplicates(vector<int>& nums) {
        int n = nums.size();
        if (n < 3) {
            return n;
        }

        int res = 2;
        for (int i = 2; i < n; ++i) {
            if (nums[res - 2] != nums[i]) {
                nums[res++] = nums[i];
            }
        }
        return res;
    }
};