Add solution #1207

Author: JoshCrozier

solutions/1207-unique-number-of-occurrences.js

@@ -0,0 +1,21 @@
+/**
+ * 1207. Unique Number of Occurrences
+ * https://leetcode.com/problems/unique-number-of-occurrences/
+ * Difficulty: Easy
+ *
+ * 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.
+ */
+
+/**
+ * @param {number[]} numbers
+ * @return {boolean}
+ */
+var uniqueOccurrences = function(numbers) {
+  const map = new Map();
+  numbers.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
+};