Unique Number of Occurrences

Given an array of integers arr, write a function that returns true if and only if the number of occurrences of each value in the array is unique.

Example 1:

Input: arr = [1,2,2,1,1,3]
Output: true
Explanation: The value 1 has 3 occurrences, 2 has 2 and 3 has 1. No two values have the same number of occurrences.

Example 2:

Input: arr = [1,2]
Output: false

Example 3:

Input: arr = [-3,0,1,-3,1,1,1,-3,10,0]
Output: true

Constraints:

1 <= arr.length <= 1000
-1000 <= arr[i] <= 1000

Solution:

class Solution {
    public boolean uniqueOccurrences(int[] arr) {
        Map<Integer, Integer> count = new HashMap();
        Set<Integer> set = new HashSet();
        for (int val : arr) {
            count.put(val, count.getOrDefault(val, 0) + 1);
        }
        for (Map.Entry<Integer, Integer> entry : count.entrySet()) {
            if (!set.add(entry.getValue())) {
                return false;
            }
        }
        return true;
    }
}