#1207 - Unique Number of Occurrences

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Problem Description

Given an array of integers arr, return true if the number of occurrences of each value in the array is unique or false otherwise.

Solution

/**
 * @param {number[]} arr
 * @return {boolean}
 */
var uniqueOccurrences = function(arr) {
  const map = new Map();
  arr.forEach(n => map.set(n, map.has(n) ? map.get(n) + 1 : 1));
  const occurrences = Array.from(map.values());
  return new Set(occurrences).size === occurrences.length;
};