(leetcode) Remove Duplicates from Sorted Array II

Follow up for "Remove Duplicates":
What if duplicates are allowed at most twice?

For example,
Given sorted array nums = [1,1,1,2,2,3],

Your function should return length = 5, with the first five elements of nums being 1, 1, 2, 2 and 3. It doesn't matter what you leave beyond the new length.

class Solution {
public:
    int removeDuplicates(vector<int>& nums) {
        int len = nums.size();
        if(!len) return len;
        int count = 1, flag = 0;
        for(int i = 1; i < len; i++) {
            if(nums[i] == nums[i - 1]) {
                count++;
            } else count = 1;
            if(count < 3) nums[++flag] = nums[i];
        }
        return flag + 1;
    }
};