Merge sort

Merge sort is an efficient, general-purpose, comparison-based sorting algorithm. Merge sort is a divide and conquer algorithm, based on the idea of breaking down a array into several subarrays until each one consists of a single element and merging those subarrays in a manner that results into a sorted array.

• Use recursion.
• If the length of the array is less than 2, return the array.
• Use Math.floor() to calculate the middle point of the array.
• Use Array.prototype.slice() to slice the array in two and recursively call mergeSort() on the created subarrays.

const mergeSort = arr => {
  if (arr.length < 2) return arr;
  const mid = Math.floor(arr.length / 2);
  const l = mergeSort(arr.slice(0, mid));
  const r = mergeSort(arr.slice(mid, arr.length));
  return Array.from({ length: l.length + r.length }, () => {
    if (!l.length) return r.shift();
    else if (!r.length) return l.shift();
    else return l[0] > r[0] ? r.shift() : l.shift();
  });
};

mergeSort([5, 1, 4, 2, 3]); // [1, 2, 3, 4, 5]

• If the length of the array is less than 2, return the array.
• Use Math.floor() to calculate the middle point of the array.
• Use Array.prototype.slice() to slice the array in two and recursively call mergeSort() on the created subarrays.
• Finally, use Array.from() and Array.prototype.shift() to combine the two sorted subarrays into one.

The algorithm has an average time complexity of O(n log n), where n is the size of the input array.

From 30-seconds-of-code: merge-sort