O(n) solution

```
public class Solution {
public int removeDuplicates(int[] nums) {
if(nums.length <= 2) {
return nums.length;
}
int index = 1;
int count = 0; //count of dup, same with preceding element
for(int i = 1; i < nums.length; i++) {
if(nums[i] != nums[i-1]) {
nums[index++] = nums[i];
count = 0;
} else if(count < 1) {
count++;
nums[index++] = nums[i];
}
}
return index;
}
}
```