Add solution #202

Author: JoshCrozier

README.md

@@ -103,6 +103,7 @@
 190|[Reverse Bits](./0190-reverse-bits.js)|Easy|
 191|[Number of 1 Bits](./0191-number-of-1-bits.js)|Easy|
 198|[House Robber](./0198-house-robber.js)|Medium|
+202|[Happy Number](./0202-happy-number.js)|Easy|
 203|[Remove Linked List Elements](./0203-remove-linked-list-elements.js)|Easy|
 204|[Count Primes](./0204-count-primes.js)|Medium|
 206|[Reverse Linked List](./0206-reverse-linked-list.js)|Easy|

solutions/0202-happy-number.js

@@ -0,0 +1,29 @@
+/**
+ * 202. Happy Number
+ * https://leetcode.com/problems/happy-number/
+ * Difficulty: Easy
+ *
+ * Write an algorithm to determine if a number n is happy.
+ *
+ * A happy number is a number defined by the following process:
+ * - Starting with any positive integer, replace the number by the sum of the squares of its digits.
+ * - Repeat the process until the number equals 1 (where it will stay), or it loops endlessly in a
+ *   cycle which does not include 1.
+ * - Those numbers for which this process ends in 1 are happy.
+ *
+ * Return true if n is a happy number, and false if not.
+ */
+
+/**
+ * @param {number} n
+ * @return {boolean}
+ */
+var isHappy = function(n) {
+  while (n !== 1) {
+    n = [...String(n)].reduce((sum, digit) => sum + digit ** 2, 0);
+    if (n === 4) {
+      return false;
+    }
+  }
+  return true;
+};