77 lines
1.4 KiB
Markdown
77 lines
1.4 KiB
Markdown
---
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title: Fibonacci sequence
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id: 597f24c1dda4e70f53c79c81
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challengeType: 5
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forumTopicId: 302268
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---
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## Description
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<section id='description'>
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Write a function to generate the <code>n<sup>th</sup></code> Fibonacci number.
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The <code>n<sup>th</sup></code> Fibonacci number is given by:
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<code>F<sub>n</sub> = F<sub>n-1</sub> + F<sub>n-2</sub></code>
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The first two terms of the series are 0 and 1.
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Hence, the series is: 0, 1, 1, 2, 3, 5, 8, 13...
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</section>
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## Instructions
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<section id='instructions'>
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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>fibonacci</code> is a function.
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testString: assert(typeof fibonacci === 'function');
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- text: <code>fibonacci(2)</code> should return a number.
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testString: assert(typeof fibonacci(2) == 'number');
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- text: <code>fibonacci(3)</code> should return 1.
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testString: assert.equal(fibonacci(3),1);
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- text: <code>fibonacci(5)</code> should return 3.
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testString: assert.equal(fibonacci(5),3);
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- text: <code>fibonacci(10)</code> should return 34.
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testString: assert.equal(fibonacci(10),34);
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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 fibonacci(n) {
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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 fibonacci(n) {
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let a = 0, b = 1, t;
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while (--n > 0) {
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t = a;
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a = b;
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b += t;
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}
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return a;
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}
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```
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</section>
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