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

set and hashmap

• Time complexity: O(N)
• Space complexity: O(N),

class Solution(object):
    def uniqueOccurrences(self, arr):
        """
        :type arr: List[int]
        :rtype: bool
        """
        hashmap = {}
        # find number of currences
        for i in arr:
            hashmap[i] = hashmap.get(i,0) + 1
        # Check the same # of currences or not

        return len(set(hashmap.values())) == len(hashmap.values())