Unique Number of Occurrences — LeetCode 1207 Python Solution

The problem

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

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.

Python solution

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

Complexity

Pattern: Hash Map

Trade memory for time: remember what you have seen so the second pass never happens. LeetCode 1207. Unique Number of Occurrences is filed here on both counts: the reference solution below belongs to the algorithm family this hub collects, and LeetCode tags it Hash Table.

The hash map guide has the Python template for the pattern and the 709 LeetCode problems that use it.

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