101 lines
2.3 KiB
Markdown
101 lines
2.3 KiB
Markdown
---
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id: 5900f3931000cf542c50fea5
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challengeType: 5
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title: 'Problem 38: Pandigital multiples'
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---
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## Description
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<section id='description'>
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Take the number 192 and multiply it by each of 1, 2, and 3:
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192 × 1 = 192
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192 × 2 = 384
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192 × 3 = 576
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By concatenating each product we get the 1 to 9 pandigital, 192384576. We will call 192384576 the concatenated product of 192 and (1, 2, 3).
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The same can be achieved by starting with 9 and multiplying by 1, 2, 3, 4, and 5, giving the pandigital, 918273645, which is the concatenated product of 9 and (1, 2, 3, 4, 5).
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What is the largest 1 to 9 pandigital 9-digit number that can be formed as the concatenated product of an integer with (1, 2, ... , <var>n</var>) where <var>n</var> > 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>pandigitalMultiples()</code> should return 932718654.
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testString: 'assert.strictEqual(pandigitalMultiples(), 932718654, "<code>pandigitalMultiples()</code> should return 932718654.");'
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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 pandigitalMultiples() {
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// Good luck!
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return true;
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}
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pandigitalMultiples();
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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 pandigitalMultiples() {
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function get9DigitConcatenatedProduct(num) {
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// returns false if concatenated product is not 9 digits
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let concatenatedProduct = num.toString();
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for (let i = 2; concatenatedProduct.length < 9; i++) {
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concatenatedProduct += num * i;
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}
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return concatenatedProduct.length === 9 ? concatenatedProduct : false;
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}
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function is1to9Pandigital(num) {
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const numStr = num.toString();
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// check if length is not 9
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if (numStr.length !== 9) {
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return false;
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}
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// check if pandigital
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for (let i = 9; i > 0; i--) {
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if (numStr.indexOf(i.toString()) === -1) {
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return false;
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}
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}
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return true;
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}
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let largestNum = 0;
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for (let i = 9999; i >= 9000; i--) {
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const concatenatedProduct = get9DigitConcatenatedProduct(i);
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if (is1to9Pandigital(concatenatedProduct) && concatenatedProduct > largestNum) {
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largestNum = parseInt(concatenatedProduct);
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break;
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}
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}
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return largestNum;
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}
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```
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</section>
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