Exercism v3 launches on Sept 1st 2021. Learn more! ๐๐๐

Published at Apr 21 2021
·
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Instructions

Test suite

Solution

An Armstrong number is a number that is the sum of its own digits each raised to the power of the number of digits.

For example:

- 9 is an Armstrong number, because
`9 = 9^1 = 9`

- 10 is
*not*an Armstrong number, because`10 != 1^2 + 0^2 = 1`

- 153 is an Armstrong number, because:
`153 = 1^3 + 5^3 + 3^3 = 1 + 125 + 27 = 153`

- 154 is
*not*an Armstrong number, because:`154 != 1^3 + 5^3 + 4^3 = 1 + 125 + 64 = 190`

Write some code to determine whether a number is an Armstrong number.

Go through the setup instructions for Javascript to install the necessary dependencies:

https://exercism.io/tracks/javascript/installation

Please `cd`

into exercise directory before running all below commands.

Install assignment dependencies:

```
$ npm install
```

Execute the tests with:

```
$ npm test
```

In the test suites all tests but the first have been skipped.

Once you get a test passing, you can enable the next one by changing `xtest`

to
`test`

.

Once you have a solution ready, you can submit it using:

```
exercism submit armstrong-numbers.js
```

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

```
import { isArmstrongNumber } from './armstrong-numbers';
describe('Armstrong Numbers', () => {
test('Zero is an Armstrong number', () => {
expect(isArmstrongNumber(0)).toEqual(true);
});
xtest('Single digit numbers are Armstrong numbers', () => {
expect(isArmstrongNumber(5)).toEqual(true);
});
xtest('There are no 2 digit Armstrong numbers', () => {
expect(isArmstrongNumber(10)).toEqual(false);
});
xtest('Three digit number that is an Armstrong number', () => {
expect(isArmstrongNumber(153)).toEqual(true);
});
xtest('Three digit number that is not an Armstrong number', () => {
expect(isArmstrongNumber(100)).toEqual(false);
});
xtest('Four digit number that is an Armstrong number', () => {
expect(isArmstrongNumber(9474)).toEqual(true);
});
xtest('Four digit number that is not an Armstrong number', () => {
expect(isArmstrongNumber(9475)).toEqual(false);
});
xtest('Seven digit number that is an Armstrong number', () => {
expect(isArmstrongNumber(9926315)).toEqual(true);
});
xtest('Seven digit number that is not an Armstrong number', () => {
expect(isArmstrongNumber(9926314)).toEqual(false);
});
});
```

```
export const isArmstrongNumber = num => [...`${num}`]
.reduce((sum, digit, _, { length }) => sum + digit ** length, 0) === num;
```

A huge amount can be learned from reading other peopleโs code. This is why we wanted to give exercism users the option of making their solutions public.

Here are some questions to help you reflect on this solution and learn the most from it.

- What compromises have been made?
- Are there new concepts here that you could read more about to improve your understanding?

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