101 lines
2.6 KiB
Markdown
101 lines
2.6 KiB
Markdown
---
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title: Self Describing Numbers
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id: 5eaf48389ee512d4d103684b
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challengeType: 5
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forumTopicId: 385289
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---
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## Description
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<section id='description'>
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There are several so-called "self describing" or <a target="_blank" href="https://en.wikipedia.org/wiki/Self-descriptive_number">"self-descriptive"</a> integers.
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An integer is said to be "self-describing" if it has the property that, when digit positions are labeled 0 to N-1, the digit in each position is equal to the number of times that digit appears in the number.
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For example, <b>2020</b> is a four-digit self describing number:
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<ul>
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<li> position 0 has value 2 and there are two 0s in the number; </li>
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<li> position 1 has value 0 and there are no 1s in the number; </li>
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<li> position 2 has value 2 and there are two 2s; </li>
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<li> position 3 has value 0 and there are zero 3s; </li>
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</ul>
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Self-describing numbers < 100,000,000 are: 1210, 2020, 21200, 3211000, 42101000.
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</section>
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## Instructions
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<section id='instructions'>
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Write a function that takes a positive integer as a parameter. If it is self-describing return true. Otherwise, return false.
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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>isSelfDescribing</code> should be a function.
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testString: assert(typeof isSelfDescribing=='function');
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- text: <code>isSelfDescribing()</code> should return a boolean.
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testString: assert(typeof isSelfDescribing(2020) =='boolean');
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- text: <code>isSelfDescribing(2020)</code> should return <code>true</code>.
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testString: assert.equal(isSelfDescribing(2020), true);
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- text: <code>isSelfDescribing(3021)</code> should return <code>false</code>.
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testString: assert.equal(isSelfDescribing(3021), false);
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- text: <code>isSelfDescribing(3211000)</code> should return <code>true</code>.
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testString: assert.equal(isSelfDescribing(3211000), true);
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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 isSelfDescribing(n) {
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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 isSelfDescribing(n) {
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let digits = String(n).split("");
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digits = digits.map(function(e) {return parseInt(e)});
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let count = digits.map((x) => {return 0})
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digits.forEach((d) =>{
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if (d >= count.length) {
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return false
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}
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count[d] += 1;
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});
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if (digits === count) {
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return true;
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}
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if (digits.length != count.length) {
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return false;
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}
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for (let i=0; i< digits.length; i++){
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if (digits[i] !== count[i]) {
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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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```
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</section>
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