Pseudo Code

Lesson 4 of 9 in Coddy's Merge Sort - DSA Series course.

mergeSort(array):
   if length(array) <= 1:
      return array
   mid = length(array) / 2
   left = mergeSort(array[0..mid])
   right = mergeSort(array[mid..end])
   return merge(left, right)

merge(left, right):
   result = []
   while left and right both still have elements:
      if left[0] <= right[0]:
         move the front of left into result
      else:
         move the front of right into result
   append whatever remains of left
   append whatever remains of right
   return result

Two functions work together:

mergeSort keeps splitting the array until the pieces are trivially sorted, then relies on merge to combine them.
merge walks two sorted lists at once, always taking the smaller front element, so the combined list stays sorted.

Try it yourself

This lesson doesn't include a code challenge.