101 lines
2.2 KiB
Markdown
101 lines
2.2 KiB
Markdown
---
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id: 5eaf48389ee512d4d103684b
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title: Self Describing Numbers
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challengeType: 5
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forumTopicId: 385289
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dashedName: self-describing-numbers
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---
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# --description--
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There are several so-called "self describing" or ["self-descriptive"](https://en.wikipedia.org/wiki/Self-descriptive_number) 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, **2020** 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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# --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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# --hints--
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`isSelfDescribing` should be a function.
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```js
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assert(typeof isSelfDescribing == 'function');
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```
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`isSelfDescribing()` should return a boolean.
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```js
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assert(typeof isSelfDescribing(2020) == 'boolean');
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```
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`isSelfDescribing(2020)` should return `true`.
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```js
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assert.equal(isSelfDescribing(2020), true);
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```
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`isSelfDescribing(3021)` should return `false`.
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```js
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assert.equal(isSelfDescribing(3021), false);
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```
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`isSelfDescribing(3211000)` should return `true`.
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```js
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assert.equal(isSelfDescribing(3211000), true);
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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 isSelfDescribing(n) {
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}
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```
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# --solutions--
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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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