New to Java

Hi Friends,
I would like to know what should be the approach to solve questions like these:

1. In an array of X elements, check to see if there are any duplicate values by providing 2 approachs:

a. to maximize-performance (0(n))
b. to minimize-memory-usage

I wrote this test program to find duplicates and now I wonder how can i change my program to follow the above said 2 approaches:

import java.util.*;
public class test{
	public static void main(String[] ar)
	{
	int[] arr = {3,5,6,4,2,3,5,2,4,2};
	StringBuffer sb = new StringBuffer();

	Arrays.sort(arr);
	boolean flag=false;

	for(int i=0;i<10;i++)
	{
		System.out.println(arr);

	}



	for(int i=0;i<9;i++)

	{

			if(arr[i]==arr[i+1]){

				if(!flag)

					sb.append(arr[i]+" ");

				flag=true;				

				continue;

			}else{		

				flag=false;

			}

	}

	System.out.println("Duplicates:"+sb.toString());

}

}





Your help would be greatly appreciated. Thanks in advance.