class Solution {
    public boolean uniqueOccurrences(int[] arr) {
        HashMap<Integer, Integer> hashMap = new HashMap<Integer, Integer>();
        HashSet<Integer> hashSet = new HashSet<Integer>();

        for (int i = 0; i < arr.length; i++) {
            if (hashMap.containsKey(arr[i])) {
                hashMap.put(arr[i], hashMap.get(arr[i]) + 1);
            }
            else {
                hashMap.put(arr[i], 1);
            }
        }

        // Note: you can also use hashMap.values() instead of having to go through the key
        for (int n : hashMap.keySet()) {
            if (hashSet.contains(hashMap.get(n))) {
                return false;
            }
            hashSet.add(hashMap.get(n));
        }

        return true;
    }
}