Merge sort

Isabelle Viktoria Maciohsek · JavaScript, Algorithm, Array, Recursion · Dec 27, 2020

Sorts an array of numbers, using the merge sort algorithm.

  • 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.
  • Finally, use Array.from() and Array.prototype.shift() to combine the two sorted subarrays into one.
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]

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