110 lines
2.5 KiB
Markdown
110 lines
2.5 KiB
Markdown
---
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title: Harshad or Niven series
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id: 595668ca4cfe1af2fb9818d4
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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>The <a href="http://mathworld.wolfram.com/HarshadNumber.html" title="link: http://mathworld.wolfram.com/HarshadNumber.html">Harshad</a> or Niven numbers are positive integers ≥ 1 that are divisible by the sum of their digits.</p><p>For example, 42 is a <a href="http://rosettacode.org/wiki/oeis:A005349" title="oeis:A005349">Harshad number</a> as 42 is divisible by (4 + 2) without remainder.</p>
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Assume that the series is defined as the numbers in increasing order.
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Task:
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<p>Implement a function to generate successive members of the Harshad sequence.</p><p>Use it to list the first twenty members of the sequence and list the first Harshad number greater than 1000.</p>
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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>isHarshadOrNiven</code> is a function.
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testString: assert(typeof isHarshadOrNiven === 'function', '<code>isHarshadOrNiven</code> is a function.');
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- text: '<code>isHarshadOrNiven()</code> should return <code>{"firstTwenty": [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 18, 20, 21, 24, 27, 30, 36, 40, 42],"firstOver1000": 1002}</code>'
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testString: 'assert.deepEqual(isHarshadOrNiven(), res, ''<code>isHarshadOrNiven()</code> should return <code>{"firstTwenty": [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 18, 20, 21, 24, 27, 30, 36, 40, 42],"firstOver1000": 1002}</code>'');'
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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 isHarshadOrNiven () {
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const res = {
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firstTwenty: [],
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firstOver1000: undefined
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};
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// Change after this line
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return res;
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}
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```
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</div>
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### After Test
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<div id='js-teardown'>
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```js
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const res = {
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firstTwenty: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 18, 20, 21, 24, 27, 30, 36, 40, 42],
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firstOver1000: 1002
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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 isHarshadOrNiven() {
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const res = {
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firstTwenty: [],
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firstOver1000: undefined
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};
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function isHarshad(n) {
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let s = 0;
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const nStr = n.toString();
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for (let i = 0; i < nStr.length; ++i) {
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s += parseInt(nStr.charAt(i), 10);
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}
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return n % s === 0;
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}
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let count = 0;
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const harshads = [];
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for (let n = 1; count < 20; ++n) {
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if (isHarshad(n)) {
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count++;
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harshads.push(n);
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}
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}
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res.firstTwenty = harshads;
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let h = 1000;
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while (!isHarshad(++h));
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res.firstOver1000 = h;
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return res;
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}
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```
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</section>
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