使用python实现二分查找

import math
def binary_search(list0, item):#list是已知的数组，item是要在list中寻找的数
    low = 0
    high = len(list0) - 1

    while low <= high:
        mid = math.floor((low + high) / 2)#Python2中有自动向下取整功能，python3中没有，所以要导入math模块中的向下取整方法math.floor
        guess = list0[mid]
        if guess == item:
            return mid
        if guess > item:
            high = mid -1
        else:
            low = mid + 1
    return None

my_list = [1, 3, 5, 7, 9]
print(binary_search(my_list, 7))
print(binary_search(my_list, 2))
            

最终运行结果：

3
None