Htykuut

i'm doing some coding exercises and i'm not being able to solve this one.

Find the sum of all divisors of a given integer.
For n = 12, the input should be
sumOfDivisors(n) = 28.

example: 1 + 2 + 3 + 4 + 6 + 12 = 28.

Constraints:
1 ≤ n ≤ 15.

how can i solve this exercise? i'm not being able to.

function(n){

    var arr = ,

        finalSum;



    if(n <= 1 || n => 16){

       return false ;   

   }

   for(var i = 0; i < n; i++){

       var tmp= n/2;

       arr.push(tmp)    

       // i need to keep on dividing n but i can't get the way of how to

   }

  return finalSum;

}

This is another way to do it:

var divisors = n=>[...Array(n+1).keys()].slice(1)

   .reduce((s, a)=>s+(!(n % a) && a), 0);



console.log(divisors(12));

JSFiddle: https://jsfiddle.net/32n5jdnb/141/

Explaining:

• 
  n=> this is an arrow function, the equivalent to function(n) {. You don't need the () if there's only one parameter.


• 
  Array(n+1) creates an empty array of n+1 elements


• 
  .keys() gets the keys of the empty array (the indexes i.e. 0, 1, 2) so this is a way to create a numeric sequence


• 
  [...Array(n+1)].keys()] uses the spread (...) operator to transform the iterator in another array so creating an array with the numeric sequence


• 
  .slice(1) removes the first element thus creating a sequence starting with 1. Remember the n+1 ?


• 
  .reduce() is a method that iterates though each element and calculates a value in order to reduce the array to one value. It receives as parameter a callback function to calculate the value and the initial value of the calculation


• 
  (s, a)=> is the callback function for reduce. It's an arrow function equivalent to function(s, a) {


• 
  s+(!(n % a) && a) is the calculation of the value.


• 
  s+ s (for sum) or the last value calculated +


• 
  !(n % a) this returns true only for the elements that have a 0 as modular value.


• 
  (!(n % a) && a) is a js 'trick'. The case is that boolean expressions in javascript don't return true or false. They return a 'truthy' or 'falsy' value which is then converted to boolean. So the actual returned value is the right value for && (considering both have to be truthy) and the first thuthy value found for || (considering only one need to be truthy). So this basically means: if a is a modular value (i.e. != 0) return a to add to the sum, else return 0.


• 
  , 0 is the initial value for the reduce calculation.

Reduce documentation: https://developer.mozilla.org/pt-BR/docs/Web/JavaScript/Reference/Global_Objects/Array/Reduce

Edit

Answering to Tristan Forward:

var divisorsList = ;

var divisors = (n)=>[...Array(n+1).keys()].slice(1)

       .reduce((s, a)=>{

          var divisor = !(n % a) && a;

          if (divisor) divisorsList.push(divisor);

          return s+divisor;

       }, 0);

    



console.log('Result:', divisors(12));

console.log('Divisors:', divisorsList);

You have to check if specified number is or not a divisor of given integer. You can use modulo % - if there's no rest, specified number is the divisor of the given integer - add it to the sum.

function sumDivisors(num){

  var sum = 0;

  for (var i = 1; i <= num; i++){

    if (!(num % i)) {

      sum += i;

    }

  }

  console.log(sum);

}



sumDivisors(6);

sumDivisors(10);