93 lines
1.8 KiB
Markdown
93 lines
1.8 KiB
Markdown
---
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title: Count the coins
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id: 59713bd26bdeb8a594fb9413
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challengeType: 5
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forumTopicId: 302238
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---
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## Description
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<section id='description'>
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There are four types of common coins in <a href="https://en.wikipedia.org/wiki/United_States" target="_blank">US</a> currency:
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<ul>
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<li>quarters (25 cents)</li>
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<li>dimes (10 cents)</li>
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<li>nickels (5 cents), and</li>
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<li>pennies (1 cent)</li>
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</ul>
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<p>There are six ways to make change for 15 cents:</p>
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<ul>
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<li>A dime and a nickel</li>
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<li>A dime and 5 pennies</li>
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<li>3 nickels</li>
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<li>2 nickels and 5 pennies</li>
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<li>A nickel and 10 pennies</li>
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<li>15 pennies</li>
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</ul>
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</section>
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## Instructions
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<section id='instructions'>
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Implement a function to determine how many ways there are to make change for a dollar using these common coins (1 dollar = 100 cents)
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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>countCoins</code> is a function.
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testString: assert(typeof countCoins === 'function');
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- text: <code>countCoints()</code> should return 242.
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testString: assert.equal(countCoins(), 242);
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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 countCoins() {
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// Good luck!
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return true;
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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 countCoins() {
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let t = 100;
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const operands = [1, 5, 10, 25];
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const targetsLength = t + 1;
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const operandsLength = operands.length;
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t = [1];
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for (let a = 0; a < operandsLength; a++) {
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for (let b = 1; b < targetsLength; b++) {
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// initialise undefined target
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t[b] = t[b] ? t[b] : 0;
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// accumulate target + operand ways
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t[b] += (b < operands[a]) ? 0 : t[b - operands[a]];
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}
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}
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return t[targetsLength - 1];
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}
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```
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</section>
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