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brunnock's solution

to Largest Series Product in the JavaScript Track

Published at Nov 24 2018 · 0 comments
Instructions
Test suite
Solution

Note:

This exercise has changed since this solution was written.

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

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.

Source

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

Submitting Incomplete Solutions

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

largest-series-product.spec.js

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

describe('Series', () => {
  test('can get the largest product of 2', () => {
    expect(largestProduct('0123456789', 2)).toBe(72);
  });

  xtest('works for a tiny number', () => {
    expect(largestProduct('19', 2)).toBe(9);
  });

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

  xtest('can get the largest product of a big number', () => {
    const largeNumber = '73167176531330624919225119674426574742355349194934969835203127745063262395783180169848018694788'
      + '51843858615607891129494954595017379583319528532088055111254069874715852386305071569329096329522744304355766896648'
      + '95044524452316173185640309871112172238311362229893423380308135336276614282806444486645238749303589072962904915604'
      + '40772390713810515859307960866701724271218839987979087922749219016997208880937766572733300105336788122023542180975'
      + '12545405947522435258490771167055601360483958644670632441572215539753697817977846174064955149290862569321978468622'
      + '48283972241375657056057490261407972968652414535100474821663704844031998900088952434506585412275886668811642717147'
      + '99244429282308634656748139191231628245861786645835912456652947654568284891288314260769004224219022671055626321111'
      + '10937054421750694165896040807198403850962455444362981230987879927244284909188845801561660979191338754992005240636'
      + '899125607176060588611646710940507754100225698315520005593572972571636269561882670428252483600823257530420752963450';
    expect(largestProduct(largeNumber, 13)).toBe(23514624000);
  });

  xtest('returns 0 if all digits are zero', () => {
    expect(largestProduct('0000', 2)).toBe(0);
  });

  xtest('returns 0 if all spans contain zero', () => {
    expect(largestProduct('99099', 3)).toBe(0);
  });

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

  xtest('rejects negative span', () => {
    expect(() => {
      largestProduct('12345', -1);
    }).toThrow(new Error('Invalid input.'));
  });

  xtest('returns 1 for empty string and zero slice length', () => {
    expect(largestProduct('', 0)).toBe(1);
  });

  xtest('returns 1 for non-empty string and zero slice length', () => {
    expect(largestProduct('123', 0)).toBe(1);
  });

  xtest('throws an error for slices bigger than the number', () => {
    expect(() => {
      largestProduct('123', 4);
    }).toThrow(new Error('Slice size is too big.'));
  });

  xtest('throws an error for empty string and non-zero slice length', () => {
    expect(() => {
      largestProduct('', 1);
    }).toThrow(new Error('Slice size is too big.'));
  });
});
function largestProduct(string,limit) {
  if ((isNaN(Number(string))) || (limit<0)) throw('Invalid input.');
  if (limit > string.length) throw('Slice size is too big.');
  if (limit===0) return 1;
  const digits = string.split('').map(Number);
  let greatest=0;
  for (let index=0; index<=digits.length-limit; ++index) {
    greatest = Math.max(greatest, digits.slice(index,index+limit).reduce( (factor,product) => factor*product));
  }
  return greatest;
}
module.exports={largestProduct};

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