1207 Unique Number of Occurrences

Given an array of integers arr, return true if the number of occurrences of each value in the array is unique, or false otherwise.

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

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class Solution:
    def uniqueOccurrences(self, arr: List[int]) -> bool:
        d = {}
        for a in arr:
            d[a] = d.get(a, 0) + 1
        counts = d.values()
        return len(counts) == len(set(counts))