LeetCode 1207. Unique Number of

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

from collections import Counter
class Solution:
    def uniqueOccurrences(self, arr: List[int]) -> bool:
        lookup = Counter(arr)
        set_a = set(arr)
        return len(set_a) == len(set(lookup.values()))

The idea is to count the number of occurrence of each element in arr and get the unique count of each number. Then we compare it with the number of unique elements. If they are the same, then it means each element has unique counts. Otherwise, we return False.
本题思路是计算arr中每个元素的出现次数，并获得每个数字的唯一计数。然后，我们将其与唯一元素的数量进行比较。如果它们相同，则意味着每个元素都有唯一的计数。否则，我们返回False。