How can I improve the performance and the readability of my function?

Question

I recently had to do a test for a job interview, and the prompt was to code a function that returns the closest number to 0 given an array of negative and positive numbers.

My function works correctly but I heard back from the recruiter saying that my function is not very performant and and that the readability was not great, here are the problem that they mentioned:

• Performances à double check (filter + sort + for + push + reserve + shift, 4 identical call to Math.abs)
• Lack of readability ( 4 if / else if)

I would like to know how I could have improved my function to make it more performant and more readable?

here's my function:

const closestToZero = (arr) => {
  // 1-a variables:
  let positiveNumbers = [];
  let negativeNumbers = [];

  // 1-b returns 0 if the input is either undefined or an empty array
  if(typeof(arr) === 'undefined' || arr.length === 0) {
    return 0
  }

  // 2- filter out non-number values then sort the array
  const onlyNumbers = arr.filter(item => typeof(item) === 'number').sort((a,b) => a-b);

  // 3- split the numbers into positive numbers and negative numbers
  for(let i = 0; i < onlyNumbers.length; i++) {
    if(onlyNumbers[i] > 0) {
      positiveNumbers.push(onlyNumbers[i])
    } else if (onlyNumbers[i] < 0) {
      negativeNumbers.push(onlyNumbers[i])
    }
  }

  // 4- reverse the negative array to get the closest to 0 at the first index
  let reversedNegativeArray = negativeNumbers.reverse()

  // 5- get rid of all the other values and keep only the closest to 0, if array empty return 0
  let closestPositiveNumber = positiveNumbers.length > 0 ? positiveNumbers.shift() : 0
  let closestNegativeNumber = reversedNegativeArray.length > 0 ? reversedNegativeArray.shift() : 0

  // 6- Compare the result of the substraction of the closestPositiveNumber and the closestNegativeNumber to find the closestToZero
  if(closestPositiveNumber - Math.abs(closestNegativeNumber) > 0 && closestNegativeNumber === 0 ) {
    return closestPositiveNumber
  } else if (closestPositiveNumber - Math.abs(closestNegativeNumber) < 0 && closestPositiveNumber === 0) {
    return closestNegativeNumber
  } else if(closestPositiveNumber - Math.abs(closestNegativeNumber) > 0) {
    return closestNegativeNumber
  } else if (closestPositiveNumber - Math.abs(closestNegativeNumber) <= 0) {
    return closestPositiveNumber
  }
}

requirements:

• if the closest number in input could be either negative or positive, the function returns the positive one
• if the input array is undefined or empty, the function returns 0

when input is [8, 5, 10] the function returns 5

when input is [5, 4, -9, 6, -10, -1, 8] the function returns -1

when input is [8, 2, 3, -2] the functions return 2

Answer 1

Although this isn't the best StackExchange forum for an "answer," Andreas does in fact give one. A solution might be like this: (pseudocode)

winner = 0      # arbitrarily assume the zeroth element is closest
for (i from 1 to array-length):
   if abs(array[i]) < abs(array[winner]):    # this one's closer ...
      winner = i

The abs() (absolute value) function is, of course, an indicator of "how close the number is to zero." abs(-3) == 3 and so on.

Answer 2

Your function is indeed very complicated. You can make good use of the Math.abs function here to clean things up quite a bit. Here is a js implementation that I would have given

test = [-1, 5, 4, -9, 6, -10, -1, 8, 1]; 


function closeToZero(arr){

    if(typeof(arr) === 'undefined' || arr.length === 0) {
        return 0;
    }

    ret = test[0]; 

    for(i = 1; i < test.length; i++){
        if(Math.abs(ret) >= Math.abs(test[i]) ){
            if(Math.abs(ret) == Math.abs(test[i])){
               ret = Math.max(ret, test[i]);
            }else{
                ret = test[i];
            }
        }
    }
    return ret; 

}

print(closeToZero(test));

Optionally you can also check for bad input if that was required

Answer 3

There's a possibility that the recruiter would have found a solution that uses reduce also unreadable.

But to extend on Andreas comment.

Here's an example snippet with a function that uses reduce, comparing the absolute values or the sign.

 const closestToZero = (arr) => { if(!arr || arr.length === 0) return 0; return arr.reduce((acc, x) => (Math.abs(x) < Math.abs(acc) || (Math.abs(x) === Math.abs(acc) && x > acc)) ? x : acc); } console.log(closestToZero()); console.log(closestToZero([])); console.log(closestToZero([8,5,10])); console.log(closestToZero([5, 4, -9, 6, -10, -1, 8])); console.log(closestToZero([8, -2, 3, 2]));