归并排序-完整实现

def merge_sort(____):
    if len(____) <= ____:
        return arr
    mid = len(____) // ____
    left = merge_sort(____)
    right = merge_sort(____)
    result = []
    i = j = ____
    while i < len(____) and j < len(____):
        if left[i] <= right[j]:
            result.append(____)
            i += ____
        else:
            result.append(____)
            j += ____
    result.extend(____)
    result.extend(____)
    return result