[leetcode] 1207. Unique Number of Occurrences

Description

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

分析

题目的意思是：给定一个数组，统计频率，如果频率的值唯一则返回True；否则返回False。这道题是一个比较简单的题目，只需要用字典统计频率，然后用set判断是否存在重复的频率就行了。

代码

class Solution:
    def uniqueOccurrences(self, arr: List[int]) -> bool:
        d=defaultdict(int)
        for val in arr:
            d[val]+=1
        s=set()
        for k,v in d.items():
            if(v not in s):
                s.add(v)
            else:
                return False
        return True