二分法

二分法效率高,但必须是有序的
lst = [1,8,16,32,55,78,89,1,5,4,7,5,9,6,8,5,4,5,44,5,2,1,4,5,1]
# [1, 1, 1, 1, 2, 4, 4, 4, 5, 5, 5, 5, 5, 5, 6, 7, 8, 8, 9, 16, 32, 44, 55, 78, 89]
lst = sorted(lst)#先排序
n = int(input("请输入一个数:"))
left = 0
right = len(lst) - 1

while left <= right: #

    mid = (left + right) // 2  # 索引只能是整数
    if n > lst[mid]:
        left = mid + 1
    elif n < lst[mid]:
        right = mid - 1
    else:
        print("在这个列表中.所在的位置%s" % mid)
        break
else:
    print("你要找的数. 不在这个序列中")

递归方法 一

def func(n, lst):
    left = 0
    right = len(lst) - 1
    if left <= right:
        mid = (left + right)//2
        if n > lst[mid]:
            new_lst = lst[mid+1:]
            return func(n, new_lst)
        elif n < lst[mid]:
            new_lst = lst[:mid]
            return func(n, new_lst)
        else:
            print("刚刚好, 在这里出现了")
            return True
    else:
        return False

lst = [1, 1, 1, 1, 2, 4, 4, 4, 5, 5, 5, 5, 5, 5, 6, 7, 8, 8, 9, 16, 32, 44, 55, 78, 89]
ret = func(88, lst)
print(ret)

递归方法 二

def func(n, lst, left=0, right=None):
    if right == None:
        right = len(lst) - 1
    if left <= right:
        mid = (left + right) // 2
        if n > lst[mid]:
            left = mid + 1
        elif n < lst[mid]:
            right = mid - 1
        else:
            return True
        return func(n, lst, left, right)
    else:
        return False


lst = [1, 1, 1, 1, 2, 4, 4, 4, 5, 5, 5, 5, 5, 5, 6, 7, 8, 8, 9, 16, 32, 44, 55, 78, 89]
ret = func(89, lst)
print(ret)