JS How can I increase the performance of this Max/Min coding challenge?

Question

I'm trying to solve some 'hackerrank.com' coding challenges. I'm stuck on this one:

You will be given an array of integers arr and a single integer k. You must create an array arr' of length k from elements of arr such that its unfairness is minimized. Unfairness is defined as max(arr') - min(arr') The function should return the minimum possible unfairness

My code works fine for the majority of test cases. However, in three of those test cases - the ones where the size of arr and k is particularly huge - fail due to an excession of the given time limit.

How can I optimize the performance of my code? Thanks in advance

function maxMin(k, arr) {
    // create array to push unfairness values to
    var unfairnesses = [];
    // sort given array in ascending order
    arr.sort(function(a, b) {
        return a - b;
    });
    // loop over sorted array    
    for(var i = 0; i < arr.length - k + 1; i++) {
        // get array with the length of k at position i
        var tempArr = arr.slice(i, i + k);
        // determine Max and Min of the sliced array
        var tempArrMax = Math.max(...tempArr);
        var tempArrMin = Math.min(...tempArr);
        // get unfairness of the sliced array
        var thisUnfairness = tempArrMax - tempArrMin;
        // push sliced-array-unfairness to unfairnesses array
        unfairnesses.push(thisUnfairness);
    }

    // return minimal value of unfairnesses array
    return Math.min(...unfairnesses);
}

Answer 1

The two first steps could be:

1. Your array is sorted. Thus there's no need to use Math.max and Math.min - the first element of a slice is the smallest, the last is the largest.
2. When you eliminate Math.max and Math.min calls, you can remove Array.prototype.slice call. Then you're left with a sort and a single pass over the array.

Answer 2

To sort the array you're already looping one time over the whole thing. Then you're looping another time to figure out which one is max and which one is the minimum.

You're looping twice as you can only loop once if you do:

function minMax(array) {
  const safeArray = array ?? []
  // No max or min as array is empty
  if(safeArray.length === 0) 
    return [undefined, undefined]

  let max: number = Number.MIN_SAFE_INTEGER
  let min: number = Number.MAX_SAFE_INTEGER
  for(let item of safeArray) {
     max = Math.max(item, max)
     min = Math.min(item, min)
  }
  return [max, min]
}