import os

def func(lujing, n):

    lst = os.listdir(lujing) # 打开文件夹,列出所有文件

    for el in lst: # el 每一个文件

        path = os.path.join(lujing, el) # 还原路径

        if os.path.isdir(path): # 判断是否是文件夹

            print('\t'*n ,el)

            func(path, n + 1)

        else:

            print('\t' * n, el)

func(r'E:\python_workspace_s18', 0)

# 二分法

lst = [1, 3, 5, 7, 13, 15, 17, 19, 21, 23, 27, 29, 31, 33, 39, 41, 43, 47, 49]

left = 0

right = len(lst) - 1

count = 1

n = int(input("请输入一个数:"))

while left <=right:

    middle = (left + right) // 2

    if n > lst[middle]:

        left = middle + 1

    elif n < lst[middle]:

        right = middle - 1

    else:

        print('找到了')

        print('循环次数为:%s' % count)

        break

    count += 1

else:

    print('不存在')

# 递归实现:

lst = [1, 3, 5, 7, 13, 15, 17, 19, 21, 23, 27, 29, 31, 33, 39, 41, 43, 47, 49]

def func(s, lst):

    left = 0

    right = len(lst) - 1

    if lst != []:

        middle = (left + right) //2

        if n > lst[middle]:

            left = middle + 1

            lst = lst[left:]

            func(s, lst)

        elif n < lst[middle]:

            right = middle -1

            lst = lst[:right]

            func(s, lst)

        else:

            print('找到了')

            return

    else:

        print('没有找到')

        return

n = int(input('请输入一个数:'))

func(n, lst)

# 递归二

lst = [1, 3, 5, 7, 13, 15, 17, 19, 21, 23, 27, 29, 31, 33, 39, 41, 43, 47, 49]

def func(n, lst, left, right):

    if left <= right:

        middle = (left + right) // 2

        if n > lst[middle]:

            left = middle + 1

            return func(n, lst, left, right)

        elif n < lst[middle]:

            right = middle - 1

            return func(n, lst, left, right) # 递归如果有返回值. 所有调用递归的地方必须写return

        else:

            print("找到了")

            return middle

    else:

        print('没有找到')

        return -1

n = int(input('请输入一个数:'))

func(n,lst,0,len(lst)-1)