how merge sort is sorted code example

Example: merge sort

# Python3 recursive merge sort algorithm -> O(n*log(n))
def merge_sort(A):
    def merge(l, r):
        i = j = 0
        n = []  # merging container
        while i < len(l) or j < len(r):

            # if no more elements to the right,
            # add remaining left elements
            if i == len(l):
                n.extend(r[j:])
                break

            # if no more elements to the left,
            # add remaining right elements
            if j == len(r):
                n.extend(l[i:])
                break

            # if elements left on both sides,
            # add smaller element
            a, b = l[i], r[j]
            if a < b:
                n.append(a)
                i += 1
            else:
                n.append(b)
                j += 1

        return n

    # divide list down to single-elements
    s = len(A)
    if s > 1:
        s //= 2
        l = merge_sort(A[:s])  # split left
        r = merge_sort(A[s:])  # split right
        return merge(l, r)  # merge sides in order
    else:
        return A