freeCodeCamp Challenge Guide: Problem 13: Large sum

Guide
#1

Problem 13: Large sum

Solutions

Solution 1 (Click to Show/Hide) 
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
}
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

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