1207. Unique Number of Occurrences

题目

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

题目大意

给你一个整数数组 arr，请你帮忙统计数组中每个数的出现次数。如果每个数的出现次数都是独一无二的，就返回 true；否则返回 false。

提示：

• 1 <= arr.length <= 1000
• -1000 <= arr[i] <= 1000

解题思路

• 给出一个数组，先统计每个数字出现的频次，判断在这个数组中是否存在相同的频次。
• 简单题，先统计数组中每个数字的频次，然后用一个 map 判断频次是否重复。