day15

递归函数：在一个函数里在调用这个函数本身。

递归的最大深度：998

def age(n):
    if n == 1:
        return 40
    else:
        return age(n-1)+2

print(age(4))

二分查找

def search(num,l,start=None,end=None):
    start = start if start else 0
    end = end if end else len(l) - 1
    mid = (end - start)//2 + start
    if start > end:
        return None
    elif l[mid] > num :
        return search(num,l,start,mid-1)
    elif l[mid] < num:
        return search(num,l,mid+1,end)
    elif l[mid] == num:
        return mid

课上讲解

def two_search(li, aim, start=0, end=None):
    end = len(li)-1 if end is None else end
    mid_index = (end - start) // 2 + start  # 3
    if start <= end:
        if li[mid_index] < aim:
            return two_search(li,aim,start=mid_index+1,end=end)
        elif li[mid_index] > aim:
            return two_search(li,aim,start=0,end=mid_index-1)  #（[2,3,5],3）
        elif li[mid_index] == aim:
            return mid_index
        else:
            return '没有此值'
    else:
        return '没有此值'