Find duplicate element in array in time O(n)

Question

I have been asked this question in a job interview and I have been wondering about the right answer.

You have an array of numbers from 0 to n-1, one o

Answer 1

//This is similar to the HashSet approach but uses only one data structure:

    int[] a = { 1, 4, 6, 7, 4, 6, 5, 22, 33, 44, 11, 5 };

    LinkedHashMap map = new LinkedHashMap();

    for (int i : a) {
        map.put(i, map.containsKey(i) ? (map.get(i)) + 1 : 1);
    }

    Set> es = map.entrySet();
    Iterator> it = es.iterator();

    while (it.hasNext()) {
        Entry e = it.next();
        if (e.getValue() > 1) {
            System.out.println("Dupe " + e.getKey());
        }
    }