Finding duplicate entries in an int[]

Question

Okay, So I need to solved the following problem.
Given an int[] or Integer[] with 1,000,000 entries. There are 2 entries out of the 1,000,000 that are duplicate. I need to find and return the duplicate entry.
Obviously iteration is out of the question given the size of the array, and converting to an arraylist would likewise not help alot.
Please offer any suggestions

Answer 1

well I tried this....
public class Main
     public static void main(String[] args)
          int list2[] = new int[1000000];
          for (int i=0; i < 1000000; i++)
               list2[i] = i;
          System.out.println(getDouble(list2));
     public static int getDouble(int[] intArray)
          ArrayList<Integer> list = new ArrayList<Integer>();
          for (int i=0; i < intArray.length; i++)
               list.add(intArray);
          for (int i=0; i < list.size(); i++)
               Integer a = list.get(i);
               if (list.indexOf(a) != list.lastIndexOf(a))
                    return list.get(i);
          return 0;
}and it takes forever.  So if you have a really fast way, a hint would be nice :-).