1207-unique-number-of-occurrences.py

"""
Problem Link: https://leetcode.com/problems/unique-number-of-occurrences/

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
"""
class Solution:
    def uniqueOccurrences(self, arr: List[int]) -> bool:
      d = {}
      for n in arr:
        d[n] = d.get(n,0) + 1
      unique = set()
      for k,v in d.items():
        if v in unique:
          return False
        unique.add(v)
      return True