2018-09-30 22:01:58 +00:00
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---
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title: Factorial
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id: 597b2b2a2702b44414742771
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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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<p>Write a function to return the factorial of a number.</p>
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<p>Factorial of a number is given by : </p>
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n! = n * (n-1) * (n-2) * ..... * 1
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<p>
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For example :
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3! = 3*2*1 = 6
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4! = 4*3*2*1 = 24
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</p>
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2018-10-08 00:01:53 +00:00
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<p>Note :
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0! = 1
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2018-09-30 22:01:58 +00:00
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</p>
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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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2018-10-04 13:37:37 +00:00
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tests:
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- text: <code>factorial</code> is a function.
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2018-10-20 18:02:47 +00:00
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testString: assert(typeof factorial === 'function', '<code>factorial</code> is a function.');
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2018-10-04 13:37:37 +00:00
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- text: <code>factorial(2)</code> should return a number.
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2018-10-20 18:02:47 +00:00
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testString: assert(typeof factorial(2) === 'number', '<code>factorial(2)</code> should return a number.');
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2018-10-04 13:37:37 +00:00
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- text: <code>factorial(3)</code> should return 6.")
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2018-10-20 18:02:47 +00:00
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testString: assert.equal(factorial(3),results[0],"<code>factorial(3)</code> should return 6.");
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2018-10-04 13:37:37 +00:00
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- text: <code>factorial(3)</code> should return 120.")
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2018-10-20 18:02:47 +00:00
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testString: assert.equal(factorial(5),results[1],"<code>factorial(3)</code> should return 120.");
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- text: <code>factorial(3)</code> should return 3,628,800.")
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testString: assert.equal(factorial(10),results[2],"<code>factorial(3)</code> should return 3,628,800.");
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2018-09-30 22:01:58 +00:00
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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 factorial (n) {
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// Good luck!
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}
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```
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</div>
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### After Test
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<div id='js-teardown'>
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```js
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2018-10-20 18:02:47 +00:00
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const results=[6,120,3628800];
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2018-09-30 22:01:58 +00:00
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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 factorial(n) {
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let sum = 1;
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while (n > 1) {
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sum *= n;
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n--;
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}
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return sum;
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}
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```
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</section>
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