2018-10-04 13:37:37 +00:00
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---
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title: Evaluate binomial coefficients
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id: 598de241872ef8353c58a7a2
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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 calculate the binomial coefficient for the given value of n and k.</p><p>This formula is recommended:</p>
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$\binom{n}{k} = \frac{n!}{(n-k)!k!} = \frac{n(n-1)(n-2)\ldots(n-k+1)}{k(k-1)(k-2)\ldots 1}$
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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>binom</code> is a function.
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2018-10-20 18:02:47 +00:00
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testString: assert(typeof binom === 'function', '<code>binom</code> is a function.');
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- text: <code>binom(5,3)</code> should return 10.
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testString: assert.equal(binom(5, 3), 10, '<code>binom(5,3)</code> should return 10.');
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- text: <code>binom(7,2)</code> should return 21.
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testString: assert.equal(binom(7, 2), 21, '<code>binom(7,2)</code> should return 21.');
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- text: <code>binom(10,4)</code> should return 210.
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testString: assert.equal(binom(10, 4), 210, '<code>binom(10,4)</code> should return 210.');
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- text: <code>binom(6,1)</code> should return 6.
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testString: assert.equal(binom(6, 1), 6, '<code>binom(6,1)</code> should return 6.');
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- text: <code>binom(12,8)</code> should return 495.
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testString: assert.equal(binom(12, 8), 495, '<code>binom(12,8)</code> should return 495.');
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2018-10-04 13:37:37 +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 binom (n, k) {
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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 binom(n, k) {
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let coeff = 1;
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for (let i = n - k + 1; i <= n; i++) coeff *= i;
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for (let i = 1; i <= k; i++) coeff /= i;
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return coeff;
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}
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```
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</section>
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