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curriculum/challenges/english/10-coding-interview-prep/rosetta-code/happy-numbers.md

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+---
+title: Happy numbers
+id: 594810f028c0303b75339ad1
+challengeType: 5
+forumTopicId: 302280
+---
+
+## Description
+<section id='description'>
+A <a href="https://en.wikipedia.org/wiki/Happy_number" target="_blank">happy number</a> is defined by the following process:
+Starting with any positive integer, replace the number by the sum of the squares of its digits, and repeat the process until the number equals <code>1</code> (where it will stay), or it loops endlessly in a cycle which does not include <code>1</code>. Those numbers for which this process ends in <code>1</code> are happy numbers, while those that do not end in <code>1</code> are unhappy numbers.
+</section>
+
+## Instructions
+<section id='instructions'>
+Implement a function that returns true if the number is happy, or false if not.
+</section>
+
+## Tests
+<section id='tests'>
+
+```yml
+tests:
+  - text: <code>happy</code> should be a function.
+    testString: assert(typeof happy === 'function');
+  - text: <code>happy(1)</code> should return a boolean.
+    testString: assert(typeof happy(1) === 'boolean');
+  - text: <code>happy(1)</code> should return true.
+    testString: assert(happy(1));
+  - text: <code>happy(2)</code> should return false.
+    testString: assert(!happy(2));
+  - text: <code>happy(7)</code> should return true.
+    testString: assert(happy(7));
+  - text: <code>happy(10)</code> should return true.
+    testString: assert(happy(10));
+  - text: <code>happy(13)</code> should return true.
+    testString: assert(happy(13));
+  - text: <code>happy(19)</code> should return true.
+    testString: assert(happy(19));
+  - text: <code>happy(23)</code> should return true.
+    testString: assert(happy(23));
+  - text: <code>happy(28)</code> should return true.
+    testString: assert(happy(28));
+  - text: <code>happy(31)</code> should return true.
+    testString: assert(happy(31));
+  - text: <code>happy(32)</code> should return true:.
+    testString: assert(happy(32));
+  - text: <code>happy(33)</code> should return false.
+    testString: assert(!happy(33));
+
+```
+
+</section>
+
+## Challenge Seed
+<section id='challengeSeed'>
+
+<div id='js-seed'>
+
+```js
+function happy(number) {
+
+}
+```
+
+</div>
+
+
+
+</section>
+
+## Solution
+<section id='solution'>
+
+
+```js
+function happy (number) {
+  let m;
+  let digit;
+  const cycle = [];
+
+  while (number !== 1 && cycle[number] !== true) {
+    cycle[number] = true;
+    m = 0;
+    while (number > 0) {
+      digit = number % 10;
+      m += Math.pow(digit, 2);
+      number = (number - digit) / 10;
+    }
+    number = m;
+  }
+  return (number === 1);
+}
+
+```
+
+</section>