92 lines
2.0 KiB
Markdown
92 lines
2.0 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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---
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## Description
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<section id='description'>
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<p>There are four types of common coins in <a href="https://en.wikipedia.org/wiki/United_States" title="link: https://en.wikipedia.org/wiki/United_States">US</a> currency:</p>
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quarters (25 cents)
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dimes (10 cents)
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nickels (5 cents), and
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pennies (1 cent)
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<p>There are six ways to make change for 15 cents:</p>
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A dime and a nickel
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A dime and 5 pennies
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3 nickels
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2 nickels and 5 pennies
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A nickel and 10 pennies
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15 pennies
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Task:
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<p>Implement a function to determine how many ways there are to make change for a dollar using these common coins? (1 dollar = 100 cents).</p>
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Reference:
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<a href="http://mitpress.mit.edu/sicp/full-text/book/book-Z-H-11.html#%_sec_Temp_52" title="link: http://mitpress.mit.edu/sicp/full-text/book/book-Z-H-11.html#%_sec_Temp_52">an algorithm from MIT Press</a>.
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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>countCoins</code> is a function.
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testString: 'assert(typeof countCoins === "function", "<code>countCoins</code> is a function.");'
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- text: <code>countCoints()</code> should return 242.
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testString: 'assert.equal(countCoins(), 242, "<code>countCoints()</code> should return 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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