递归函数

递归函数    了解什么是递归  ： 在函数中调用自身函数        最大递归深度默认是997/998 —— 是python从内存角度出发做得限制

　　递归的缺点 ： 占内存　　递归的优点：  会让代码变简单

# alex 多大       n = 1   age(1) = age(2)+2 = age(n+1) + 2
# alex比egon大两岁
# egon多大？      n = 2   age(2) = age(3) + 2 = age(n+1) +2
# egon比wusir大两岁
# wusir多大       n = 3   age(3) = age(4) + 2 = age(n+1) +2
# wusir比金老板大两岁
# 金老板多大？
# 金老板40了      n = 4   age(4) = 40

# n = 4 age(4) = 40
# n <4  age(n) = age(n+1) +2
def age(n):
    if n == 4:
        return 40
    elif n >0 and n < 4:
        age(n+1) + 2
#
print(age(1))

# # 教你看递归
# def age(1):
#     if 1 == 4:
#         return 40
#     elif 1 > 0 and 1 < 4:
#         return 46
#
# def age(2):
#     if 2 == 4:
#         return 40
#     elif 2 >0 and 2 < 4:
#         age(3) + 2    None +2
#
# def age(3):
#     if 3 == 4:
#         return 40
#     elif 3 >0 and 3 < 4:
#         42
#
# def age(4):
#     if 4 == 4:
#         return 40
#     elif n >0 and n < 4:
#         age(n+1) + 2

二分查找算法

了解基础的算法 才能创造出更好的算法不是所有的事情都能套用现成的方法解决的有些时候会用到学过的算法知识来解决新的问题

# 二分查找算法 必须处理有序的列表
# l = [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]
# 5000000  4999998
# 代码实现
# def find(l,aim):
#     mid_index = len(l) // 2
#     if l[mid_index] < aim:
#         new_l = l[mid_index+1 :]
#         find(new_l,aim)
#     elif l[mid_index] > aim:
#         new_l = l[:mid_index]
#         find(new_l, aim)
#     else:
#         print(‘找到了‘,mid_index,l[mid_index])
#
# find(l,66)

l = [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 find(l,aim,start = 0,end = None):
#     end = len(l) if end is None else end   # end = len(l)   24
#     mid_index = (end - start)//2 + start   #计算中间值  12 + 0 = 12
#     if l[mid_index] < aim:       #l[12] < 44   #41 < 44
#         find(l,aim,start =mid_index+1,end=end)  # find(l,44,start=13,end=24)
#     elif l[mid_index] > aim:
#         find(l, aim, start=start, end=mid_index-1)
#     else:
#         print(‘找到了‘,mid_index,aim)
#
# def find(l,aim,start = 0,end = None):    # l,44,start=13,end=24
#     end = len(l) if end is None else end   # end = 24
#     mid_index = (end - start)//2 + start   #计算中间值  24-13/2 = 5 + 13 = 18
#     if l[mid_index] < aim:       #l[18] < 44   #67 < 44
#         find(l,aim,start =mid_index+1,end=end)
#     elif l[mid_index] > aim:     # 67 > 44
#         find(l, aim, start=start, end=mid_index-1)  # find(l,44,start=13,end=17)
#     else:
#         print(‘找到了‘,mid_index,aim)
#
# def find(l,aim,start = 0,end = None):    # l,44,start=13,end=17
#     end = len(l) if end is None else end   # end = 17
#     mid_index = (end - start)//2 + start   #计算中间值  17-13/2 = 2 + 13 = 15
#     if l[mid_index] < aim:       #l[15] < 44   #55 < 44
#         find(l,aim,start =mid_index+1,end=end)
#     elif l[mid_index] > aim:     # 55 > 44
#         find(l, aim, start=start, end=mid_index-1)  # find(l,44,start=13,end=14)
#     else:
#         print(‘找到了‘,mid_index,aim)
#
# def find(l,aim,start = 0,end = None):    # l,44,start=13,end=14
#     end = len(l) if end is None else end   # end = 14
#     mid_index = (end - start)//2 + start   #计算中间值  14-13/2 = 0+ 13 = 13
#     if l[mid_index] < aim:       #l[13] < 44   #42 < 44
#         find(l,aim,start =mid_index+1,end=end)  # find(l,44,start=14,end=14)
#     elif l[mid_index] > aim:     # 42 > 44
#         find(l, aim, start=start, end=mid_index-1)
#     else:
#         print(‘找到了‘,mid_index,aim)

def find(l,aim,start = 0,end = None):
    end = len(l) if end is None else end
    mid_index = (end - start)//2 + start
    if start <= end:
        if l[mid_index] < aim:
            return find(l,aim,start =mid_index+1,end=end)
        elif l[mid_index] > aim:
            return find(l, aim, start=start, end=mid_index-1)
        else:
            return mid_index
    else:
        return ‘找不到这个值‘


ret= find(l,44)
print(ret)