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Computer Science Introduction to Data Structures The Merge Sort Algorithm Alternate Versions of Merge Sort

I would like JavaScript Version of Everything in this course, and the Algorithm Courses.

The email provided doesn't work, and numerous students from various tracks, studying various languages, have been asking for these lessons in their language of choice for years now. I've seen staff only chime in to tell students to send the issue to the support staff. Several have claimed to have done so, and no effort has been made to remedy this pervasive issue.

Chris Freeman
Chris Freeman
Treehouse Moderator 68,423 Points

To help your case, I will mark this post feedback. (A Mod can do this if the post links to the topic material. Thanks!)

1 Answer

Erland Van Olmen
.a{fill-rule:evenodd;}techdegree seal-36
Erland Van Olmen
Full Stack JavaScript Techdegree Graduate 17,825 Points

I made a simple implementation of Merge Sort in JavaScript, hope it helps whoever wants something to play with. It is not optimized in any way though.

// function to fill an array 'list' with the amount 'numValues' of values
// between 0 and maxVal (excluding maxVal):
function fillUnsorted(list, numValues) {
  const maxVal = 16;
  for (let i = 0; i < numValues; i++) {
    list.push(Math.trunc(Math.random() * maxVal));
  return list;

function mergeSort(list) {
  let listA = [];
  let listB = [];
  const len = list.length;
  if(len > 1) {
    const halfLen = Math.trunc(len / 2);
    listA = mergeSort(list.slice(0, halfLen));
    listB = mergeSort(list.slice(halfLen));
  } else {
    return list;
  // merge both lists together:
  let indexA = 0; 
  let indexB = 0;
  let destList = [];
  while (indexA < listA.length && indexB < listB.length) {
    if (listA[indexA] < listB[indexB]) {
    } else {
  if (indexA < listA.length) {
    destList = [...destList, ...listA.slice(indexA)];
  } else if (indexB < listB.length) {
    destList = [...destList, ...listB.slice(indexB)];
  return destList;

let unsorted = [];
fillUnsorted(unsorted, 13);
console.log('Unsorted list: ', unsorted);
console.log('Sorted list: ', mergeSort(unsorted));