How to efficiently remove duplicates from an array without using Set

Question

I was asked to write my own implementation to remove duplicated values in an array. Here is what I have created. But after tests with 1,000,000 elements it took very long ti

Answer 1

public static int[] removeDuplicates(int[] arr){
    HashSet set = new HashSet<>();
    final int len = arr.length;
    //changed end to len
    for(int i = 0; i < len; i++){
        set.add(arr[i]);
    }

    int[] whitelist = new int[set.size()];
    int i = 0;
    for (Iterator it = set.iterator(); it.hasNext();) {
        whitelist[i++] = it.next();
    }
    return whitelist;
}

Runs in O(N) time instead of your O(N^3) time