python递归函数及二分法查找

死循环: 可以无限循环,不会停止
while True:
    print(‘我不是递归‘)
 
递归: 不是死循环,有最大循环深度
def story():
    print(‘我是递归‘)
    story()
story()
超过了递归的最大深度报错
RecursionError: maximum recursion depth exceeded while calling a Python object

n = 0
def func():
    global n
    n += 1
    print(n)
    func()
func()
import sys
print(sys.getrecursionlimit())    #查看递归的最大深度

如果你的递归每次都要超过限制 不适合用递归来解决
为什么要有限制? 内存消耗的保护机制
设置递归的最大深度
import sys
sys.setrecursionlimit(1000000)

n = 0
def func():
    global n
    n += 1
    print(n)
    func()
func()

案例(遍历树形结构)
import os
def func(lujing,n):
    lst = os.listdir(lujing)    #打开文件夹,列出该文件夹中的所有文件及目录
    for i in lst:               #循环文件夹中的所有名字,i相当于文件名
        path = os.path.join(lujing,i)   #拼接循环的文件名路径
        # print(path)
        if os.path.isdir(path): #判断拼接后的路径是否是目录
            print(‘\t‘*n,i)       #如果是目录就打印,n等于几就是几个tab键分隔
            func(path,n+1)          #然后再次调用自己,在重复上面的操作,
        else:
            print(‘\t‘*n,i)       #如果不是目录,就打印文件名
func(‘E:/test/‘,0)  #0为分层间隔

lst = [2,3,5,10,15,16,18,22,26,30,32,35,41,42,43,55,56,66,67,69,72,76,82,83,88]
print(len(lst))
n = int(input(‘<<<<:‘))
start = 0
end = len(lst) -1
count = 0
while start <= end:
    mid = (start + end) // 2
    count+= 1
    if n > lst[mid]:
        start = mid +1
    elif n < lst[mid]:
        end = mid -1
    else:
        print(‘存在‘)
        break
else:
    print(‘不存在‘)
print(‘查找了%s次‘%count)

方法2
lst = [2,3,5,10,15,16,18,22,26,30,32,35,41,42,43,55,56,66,67,69,72,76,82,83,88]
def func(n,lst):
    start = 0
    end = len(lst) -1
    # count = 0
    if lst != []:
        mid = (start + end) //2
        if n > lst[mid]:
            func(n,lst[mid+1:])
        elif n < lst[mid]:
            func(n,lst[:mid])
        else:
            print(‘存在‘)
            return
    else:
        print(‘不存在‘)
        return
n = int(input(‘<<<:‘))
func(n,lst)

方法3
lst = [2,3,5,10,15,16,18,22,26,30,32,35,41,42,43,55,56,66,67,69,72,76,82,83,88]
def func(n,lst,start,end):
    if start <= end:
        mid = (start + end) //2
        if n > lst[mid]:
            start = mid + 1
            return func(n,lst,start,end)
        elif n < lst[mid]:
            end = mid - 1
            return func(n,lst,start,end)
        else:
            print(‘找到了‘)
            return mid
    else:
        print(‘找不到‘)
        return -1
n = int(input(‘<<:‘))
ret = func(n,lst,0,len(lst)-1)
print(ret)

#最快的查找
lst = [2,3,5,10,15,16,18,22,26,30,32,35,41,42,43,55,56,66,67,69,72,76,82,83,88]
new_lst = []
for i in range(88):
    new_lst.append(0)
for i in lst:
    new_lst[i] = 1
print(new_lst)
i = int(input(‘<<<:‘))
if new_lst[i] == 0:
    print(‘存在‘)
else:
    print(‘不存在‘)