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## to Largest Series Product in the JavaScript Track

Published at Mar 20 2021 · 0 comments
Instructions
Test suite
Solution

Given a string of digits, calculate the largest product for a contiguous substring of digits of length n.

For example, for the input `'1027839564'`, the largest product for a series of 3 digits is 270 (9 * 5 * 6), and the largest product for a series of 5 digits is 7560 (7 * 8 * 3 * 9 * 5).

Note that these series are only required to occupy adjacent positions in the input; the digits need not be numerically consecutive.

For the input `'73167176531330624919225119674426574742355349194934'`, the largest product for a series of 6 digits is 23520.

## Setup

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

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

## Requirements

Please `cd` into exercise directory before running all below commands.

Install assignment dependencies:

``````\$ npm install
``````

## Making the test suite pass

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`.

## Submitting Solutions

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

``````exercism submit largest-series-product.js
``````

## Submitting Incomplete Solutions

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

## Exercise Source Credits

A variation on Problem 8 at Project Euler http://projecteuler.net/problem=8

### largest-series-product.spec.js

``````import { largestProduct } from './largest-series-product';

describe('Largest Series Product', () => {
test('finds the largest product if span equals length', () => {
expect(largestProduct('29', 2)).toEqual(18);
});

xtest('can find the largest product of 2 with numbers in order', () => {
expect(largestProduct('0123456789', 2)).toEqual(72);
});

xtest('can find the largest product of 2', () => {
expect(largestProduct('576802143', 2)).toEqual(48);
});

xtest('can find the largest product of 3 with numbers in order', () => {
expect(largestProduct('0123456789', 3)).toEqual(504);
});

xtest('can find the largest product of 3', () => {
expect(largestProduct('1027839564', 3)).toEqual(270);
});

xtest('can find the largest product of 5 with numbers in order', () => {
expect(largestProduct('0123456789', 5)).toEqual(15120);
});

xtest('can get the largest product of a big number', () => {
expect(
largestProduct('73167176531330624919225119674426574742355349194934', 6)
).toEqual(23520);
});

xtest('reports zero if the only digits are zero', () => {
expect(largestProduct('0000', 2)).toEqual(0);
});

xtest('reports zero if all spans include zero', () => {
expect(largestProduct('99099', 3)).toEqual(0);
});

xtest('rejects span longer than string length', () => {
expect(() => largestProduct('123', 4)).toThrow(
new Error('Span must be smaller than string length')
);
});

xtest('reports 1 for empty string and empty product (0 span)', () => {
expect(largestProduct('', 0)).toEqual(1);
});

xtest('reports 1 for nonempty string and empty product (0 span)', () => {
expect(largestProduct('123', 0)).toEqual(1);
});

xtest('rejects empty string and nonzero span', () => {
expect(() => largestProduct('', 1)).toThrow(
new Error('Span must be smaller than string length')
);
});

xtest('rejects invalid character in digits', () => {
expect(() => largestProduct('1234a5', 2)).toThrow(
new Error('Digits input must only contain digits')
);
});

xtest('rejects negative span', () => {
expect(() => largestProduct('12345', -1)).toThrow(
new Error('Span must be greater than zero')
);
});
});``````
``````// exercism --> largest series product
// Given a string of digits, calculate the largest product for a contiguous substring of digits of length n.
// For example, for the input '1027839564', the largest product for a series of 3 digits is 270 (9 * 5 * 6), and the largest product for a series of 5 digits is 7560 (7 * 8 * 3 * 9 * 5).
// Note that these series are only required to occupy adjacent positions in the input; the digits need not be numerically consecutive.
// For the input '73167176531330624919225119674426574742355349194934', the largest product for a series of 6 digits is 23520.

export const largestProduct = (series, span) => {
if (span === 0) {
return 1;
}
if (series.length < span) {
throw new Error("Span must be smaller than string length");
}
if (series.match(/[a-z]/g)) {
throw new Error("Digits input must only contain digits");
}
if (span < 0) {
throw new Error("Span must be greater than zero");
}
const subseriesArray = [];
for (let i = 0; i < series.length - 1; i++) {
const subseries = series.substring(i, i + span);
if (subseries.length === span) {
subseriesArray.push(subseries);
}
}
return Math.max(
...subseriesArray.map((subseries) =>
subseries.split("").reduce((acc, curr) => acc * curr, 1)
)
);
};

// -----1st attempt-----(did not pass test: 'can get the largest product of a big number')
// export const largestProduct = (series, span) => {
//   if (span === 0) {
//     return 1;
//   }
//   if (series.length < span) {
//     throw new Error("Span must be smaller than string length");
//   }
//   if (series.match(/[a-z]/g)) {
//     throw new Error("Digits input must only contain digits");
//   }
//   if (span < 0) {
//     throw new Error("Span must be greater than zero");
//   }
//   let product = [];
//   let numSeries = series.split("").map((x) => parseInt(x));

//   if (series.length === span) {
//     product.push(numSeries.reduce((i, curr) => i * curr));
//     return product
//       .slice(0, series.length - 1)
//       .sort()
//       .pop();
//   } else {
//     let collectionOfSeries = numSeries
//       .map((index) => numSeries.slice(index, index + span))
//       .filter((x) => x.length === span);
//     for (let i = 0; i < collectionOfSeries.length; i++) {
//       product.push(collectionOfSeries[i].reduce((acc, curr) => acc * curr, 1));
//     }

//     return product.reduce((prev, curr) => (prev > curr ? prev : curr));
//   }
// };``````

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