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

Solution(javascript)

/**
 * @param {number[]} arr
 * @return {boolean}
 */
var uniqueOccurrences = function(arr) {
    const m = new Map();
    arr.forEach((e) => m.set(e, m.get(e)? m.get(e) + 1 : 1));
    return m.size === new Set([...m.values()]).size;
};