python归并排序的基本思路

# 归并排序

def merge_sort(alist):

    '''归并排序'''

    n = len(alist)

    if n <= 1:

        return alist

    else:

        mid = n // 2

        # left 表示采用归并排序后形成的有序的新的列表

        left_li = merge_sort(alist[:mid])

        # right 表示采用归并排序后形成的有序的新的列表

        right_li = merge_sort(alist[mid:])

        # 将两个有序的子序列合并成一个新的整体

        # merge(left,right)

        left_pointer,right_pointer = 0,0

        result = []

        while left_pointer < len(left_li) and right_pointer < len(right_li):

            if left_li[left_pointer] <= right_li[right_pointer]:

                result.append(left_li[left_pointer])

                left_pointer += 1

            else:

                result.append(right_li[right_pointer])

                right_pointer += 1

        result += left_li[left_pointer:]

        result += right_li[right_pointer:]

        return result

if __name__ == '__main__':

    alist = [54, 26, 93, 17, 77, 31, 44, 55, 20]

    print(alist)

    sorted_alist = merge_sort(alist)

    print(sorted_alist)