Well, an extension of Remove Duplicates from Sorted Array.

The program is fairly similar to that in .

1     int removeDuplicates(vector
     
      & nums) {2         if (nums.size() <= 2) return nums.size();3         int pos = 1;4         for (int i = 2; i < nums.size(); i++)5             if (nums[i] != nums[pos] || nums[i] != nums[pos - 1])6                 nums[++pos] = nums[i];7         return pos + 1;8     }
     

After playing with it for a while, you may notice that the code can be easily extended to accommodate 3, 4, ... duplicates by modifying lines 3, 4, 5 in a similar manner.