gistfile1.txt

public class Rare {
    public static int nthMostRare(int[] elements, int n) {
        final Map<Integer, Integer> map = new HashMap<>();
        for (int i: elements)
        {
            map.compute(i, (k, v) -> {
                if (k == null) {
                    return 1;
                } else {
                    if (v == null) return 1;
                    return v+1;
                }
            });
        }
        Map<Integer, Integer> remap  = sortByValue(map);
        System.out.println(remap);
        return (Integer) remap.keySet().toArray()[n-1];
    }

    public static <K, V extends Comparable<? super V>> Map<K, V> sortByValue(Map<K, V> map) {
        List<Map.Entry<K, V>> list = new ArrayList<>(map.entrySet());
        list.sort(Map.Entry.comparingByValue());

        Map<K, V> result = new LinkedHashMap<>();
        for (Map.Entry<K, V> entry : list) {
            result.put(entry.getKey(), entry.getValue());
        }

        return result;
    }

    public static void main(String[] args) {
        int x = nthMostRare(new int[] { 5, 4, 3, 2, 1, 5, 4, 3, 2, 5, 4, 3, 5, 4, 5 }, 2);
        System.out.println(x);
    }
}