I'm currently training on codewars, and today was multiples of 3 and 5. I tried with a casual solution using reduce ternary, and it worked.

I then tried to solve it with recusrive function. Instructions are as follow :

If we list all the natural numbers below 10 that are multiples of 3 or 5, we get 3, 5, 6 and 9. The sum of these multiples is 23.

Finish the solution so that it returns the sum of all the multiples of 3 or 5 below the number passed in. Additionally, if the number is negative, return 0 (for languages that do have them).

Link is here

wiki

const input = 10

function sum35(num){
  num = num - 1
  const lastThree = num - num%3
  const threeQuantity = lastThree/3
  
  const lastFive = num - num%5
  const fiveQuantity = lastFive/5
  
  return getSum(threeQuantity,3,lastThree)   getSum(fiveQuantity, 5, lastFive)
  
  function getSum(n, first, last) {
   return (n/2)*(first   last)
  }
}

console.log(sum35(10))

CodePudding user response：

Defining res as a global is very likely the problem: its value will be reused for subsequent calls of the function.

Change your function to take res as a parameter. If the signature must define only a single parameter, using an inner function would be an idea.

Here's a solution using a nested function, simplifying some of the unnecessary complications and duplications:

function solution(n) {
    let res = 0;

    function _solution(n) {
        if(n <= 0) {
            return 0;
        }

        if(n % 3 != 0 && n % 5 != 0) {
            return _solution(n - 1);
        }

        res  = n;
        _solution(n - 1);
        return res;
    }

    return _solution(n - 1);
}

But note that this is not a "clean" recursive approach, because the function is actually a closure and has a side-effect: modifying the value of the outside variable res. For a proper recursive implementation, see yanai edri's answer.