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].

分析：从第三个数开始，每个数都只和它前面第二个数相比较，如果不同的话，则在结果中添加该数；如果相同，则不处理。运行时间21ms

 1 class Solution {
 2 public:
 3     int removeDuplicates(int A[], int n) {
 4         if(n <= 2) return n;
 5         
 6         int index = 2;
 7         for(int i = 2; i < n; i++){
 8             if(A[i] != A[index-2]) A[index++] = A[i];
 9         }
10         return index;
11     }
12 };