python 归并排序

#! coding=utf-8


def merge_sort(arr):
    lenght = len(arr)
    if lenght <= 1:
        return arr

    num = int(lenght / 2 )
    left = merge_sort(arr[num:])
    right = merge_sort(arr[:num])

    return merge(left,right)


def merge(left,right):

    r,l = 0,0
    result = []
    while l <len(left) and r < len(right):
        if left[l] <= right[r]:
            result.append(left[l])
            l += 1
        else:
            result.append(right[r])
            r += 1

    result += list(left[l:])
    result += list(right[r:])
    return result

if __name__ == '__main__':
    # 如果多条list进行归并排序,那么在外部将其合并为一个无序list
    li = [6,5,9,23,24,6,1,4,154,26,9,1,414,21,52,185,31,13]
    print(merge_sort(li))
    # [1, 1, 4, 5, 6, 6, 9, 9, 13, 21, 23, 24, 26, 31, 52, 154, 185, 414]