< Back 1207. Unique Number of Occurrences For this one, we're returning a boolean if the frequency of each integer within the input array is unique. The solution is as follows: from collections import Counter class Solution: def uniqueOccurrences(self, arr: List[int]) -> bool: counts = Counter(arr).values() return len(counts) == len(set(counts)) _ Time Complexity: O(n) - We have to iterate through the entire input array to count frequencies. _ Space Complexity: O(n) - We store the frequency of each number in the input array.