97 lines
3.1 KiB
Markdown
97 lines
3.1 KiB
Markdown
---
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title: Happy numbers
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id: 594810f028c0303b75339ad1
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challengeType: 5
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---
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## Description
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<section id='description'>
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A <a href="https://en.wikipedia.org/wiki/Happy_number" target="_blank">happy number</a> is defined by the following process:
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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.
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</section>
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## Instructions
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<section id='instructions'>
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Implement a function that returns true if the number is happy, or false if not.
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</section>
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## Tests
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<section id='tests'>
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```yml
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tests:
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- text: <code>happy</code> is a function.
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testString: assert(typeof happy === 'function', '<code>happy</code> is a function.');
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- text: <code>happy(1)</code> should return a boolean.
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testString: assert(typeof happy(1) === 'boolean', '<code>happy(1)</code> should return a boolean.');
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- text: <code>happy(1)</code> should return true.
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testString: assert(happy(1), '<code>happy(1)</code> should return true.');
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- text: <code>happy(2)</code> should return false.
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testString: assert(!happy(2), '<code>happy(2)</code> should return false.');
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- text: <code>happy(7)</code> should return true.
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testString: assert(happy(7), '<code>happy(7)</code> should return true.');
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- text: <code>happy(10)</code> should return true.
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testString: assert(happy(10), '<code>happy(10)</code> should return true.');
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- text: <code>happy(13)</code> should return true.
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testString: assert(happy(13), '<code>happy(13)</code> should return true.');
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- text: <code>happy(19)</code> should return true.
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testString: assert(happy(19), '<code>happy(19)</code> should return true.');
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- text: <code>happy(23)</code> should return true.
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testString: assert(happy(23), '<code>happy(23)</code> should return true.');
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- text: <code>happy(28)</code> should return true.
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testString: assert(happy(28), '<code>happy(28)</code> should return true.');
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- text: <code>happy(31)</code> should return true.
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testString: assert(happy(31), '<code>happy(31)</code> should return true.');
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- text: <code>happy(32)</code> should return true:.
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testString: assert(happy(32), '<code>happy(32)</code> should return true:.');
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- text: <code>happy(33)</code> should return false.
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testString: assert(!happy(33), '<code>happy(33)</code> should return false.');
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```
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</section>
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## Challenge Seed
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<section id='challengeSeed'>
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<div id='js-seed'>
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```js
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function happy(number) {
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// Good luck!
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}
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```
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</div>
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</section>
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## Solution
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<section id='solution'>
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```js
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function happy (number) {
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let m;
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let digit;
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const cycle = [];
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while (number !== 1 && cycle[number] !== true) {
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cycle[number] = true;
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m = 0;
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while (number > 0) {
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digit = number % 10;
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m += Math.pow(digit, 2);
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number = (number - digit) / 10;
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}
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number = m;
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}
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return (number === 1);
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}
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```
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</section>
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