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 A = [1,1,1,2,2,3],

Your function should return length = 5, and A is now [1,1,2,2,3].

int removeDuplicates(int A[], int n) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if(n<=2 || A==NULL)return n;
		int res = 1;
		int pre = A[0];
		bool twice = false;
		for(int i=1;i<n;i++)
		{
			if(A[i]==pre && twice)
				continue;
			else if(A[i]==pre)
			{
				A[res] = A[i];
				res++;
				twice=true;
			}else{
				A[res]=A[i];
				res++;
				pre = A[i];
				twice = false;
			}
		}
		return res;
    }