94 lines
1.7 KiB
Markdown
94 lines
1.7 KiB
Markdown
---
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id: 59713bd26bdeb8a594fb9413
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title: Count the coins
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challengeType: 5
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forumTopicId: 302238
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dashedName: count-the-coins
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---
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# --description--
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There are four types of common coins in [US](https://en.wikipedia.org/wiki/United_States) 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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# --instructions--
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Implement a function to determine how many ways there are to make change for a given input, `cents`, that represents an amount of US pennies using these common coins.
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# --hints--
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`countCoins` should be a function.
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```js
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assert(typeof countCoins === 'function');
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```
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`countCoins(15)` should return `6`.
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```js
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assert.equal(countCoins(15), 6);
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```
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`countCoins(85)` shouls return `163`.
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```js
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assert.equal(countCoins(85), 163);
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```
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`countCoins(100)` should return `242`.
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```js
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assert.equal(countCoins(100), 242);
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```
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# --seed--
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## --seed-contents--
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```js
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function countCoins(cents) {
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return true;
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}
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```
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# --solutions--
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```js
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function countCoins(cents) {
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const operands = [1, 5, 10, 25];
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const targetsLength = cents + 1;
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const operandsLength = operands.length;
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const 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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