Unique Number of Occurrences

1class Solution {
2    public boolean uniqueOccurrences(int[] arr) {
3        HashMap<Integer, Integer> hashMap = new HashMap<Integer, Integer>();
4        HashSet<Integer> hashSet = new HashSet<Integer>();
5
6        for (int i = 0; i < arr.length; i++) {
7            if (hashMap.containsKey(arr[i])) {
8                hashMap.put(arr[i], hashMap.get(arr[i]) + 1);
9            }
10            else {
11                hashMap.put(arr[i], 1);
12            }
13        }
14
15        // Note: you can also use hashMap.values() instead of having to go through the key
16        for (int n : hashMap.keySet()) {
17            if (hashSet.contains(hashMap.get(n))) {
18                return false;
19            }
20            hashSet.add(hashMap.get(n));
21        }
22
23        return true;
24    }
25}