Remove duplicates from sorted array

import java.util.*;
public class Solution {
	public static int removeDuplicates(ArrayList<Integer> arr,int n) {
		// Write your code here.
		HashSet<Integer>set=new HashSet<>();
		for(int i=0;i<n;i++)
		{
			set.add(arr.get(i));
		}return set.size();
	}
}