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replaced stub with solution to large sum (#36618) 

replaced stub with solution to large sum, explanation, links
pull/36600/head
alan1001110 2019-08-17 05:40:54 -07:00 committed by Randell Dawson
parent 56d78a1119
commit b4ef20d716
1 changed files with 29 additions and 3 deletions
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guide/english/certifications/coding-interview-prep/project-euler/problem-13-large-sum/index.md
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---
title: Large sum
---
## Problem 13: Large sum
Challenge: Work out the first ten digits of the sum of one-hundred 50-digit numbers.
This is a stub. <a href='https://github.com/freecodecamp/guides/tree/master/src/pages/certifications/coding-interview-prep/project-euler/problem-13-large-sum/index.md' target='_blank' rel='nofollow'>Help our community expand it</a>.
## Spoiler Alert!
<a href='https://github.com/freecodecamp/guides/blob/master/README.md' target='_blank' rel='nofollow'>This quick style guide will help ensure your pull request gets accepted</a>.
## One Solution:
```
function largeSum(arr) {
let sum = arr.reduce((acc, item) => acc + Number(item), 0); // 8.348422521139211e+49
let str = sum.toString().split('e')[0]; // '8.348422521139211'
return 1e+9 * str.slice(0,11); // 8348422521
}
<!-- The article goes here, in GitHub-flavored Markdown. Feel free to add YouTube videos, images, and CodePen/JSBin embeds -->
const testNums = [
'37107287533902102798797998220837590246510135740250',
'46376937677490009712648124896970078050417018260538'
];
largeSum(testNums);
```
### Code Explanation:
* The function receives an array of strings
* The first line converts the strings to numbers and adds them
* The second line converts the large sum to a string with toString, then gets everything to the left of 'e' using String.split().
* The third line multiplies 1,000,000,000 by the first 11 characters to implicitly coerce the string to a 10 digit number
* Note: One regular expression could accomplish the same task as the second and third lines together
### Resources
* <a href='https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/reduce' target='_blank' rel='nofollow'>Array.reduce()</a>
* <a href='https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/split' target='_blank' rel='nofollow'>String.split()</a>