class Solution {
    
    // 고유한 발생 수
    // T: O(n)
    // S: O(n)
    public boolean uniqueOccurrences(int[] arr) {
        // Store the frequency of elements in the unordered map.
        Map<Integer, Integer> freq = new HashMap<>();
        
        for (int num : arr) {
            freq.put(num, freq.getOrDefault(num, 0) + 1);
        }
        
        // Store the frequency count of elements in the unordered set.
        Set<Integer> freqSet = new HashSet<>(freq.values());
        
        // If the set size is equal to the map size, 
        // It implies frequency counts are unique.
        return freq.size() == freqSet.size();
    }
}