【求答疑】python实现二分查找 找不到数组中的数

[key_1997]

python实现二分查找 找不到数组中的数，代码和运行结果贴在下面了，希望大佬们能帮我指出错误

def binary_search(find,array):
    low = 0
    high = len(array)-1
    while low < high:
        mid = (low + high)/2
        if find == mid:
            return mid
        elif find < mid:
            high = mid-1
        else:
            low = mid+1

    print('not found')

if __name__ == '__main__':
    list = [1,2,3,4,5,6,7,8,9]
    num = 6
    location = binary_search(num,list)
    print (location)

运行结果：E:\python练习\demo\venv\Scripts\python.exe E:/python练习/demo/排序算法/binary_search.py
not found
None

Process finished with exit code 0

[key_1997]

[quote=引用 2 楼 hbu_pig 的回复:]
楼主您好，刚才试了一下您回复的代码，我发现是我在给mid赋值的时候没有转成int型，但是我不明白为什么要转？
还有就是在比较的时候直接可以find<mid
而不是find< array[mid] mid就是数组中的一个值，如果按照您那样写的话，数组的索引从0开始，那么查到的数就是他的下一位数了

[key_1997]

引用 2 楼 hbu_pig 的回复:

def binary_search(find,array):
    low = 0
    high = len(array)-1
    while low <= high:
        mid = (int)((low + high)/2)
        if find == array[mid]:
            return mid
        elif find < array[mid]:
            high = mid-1
        else:
            low = mid+1

    print('not found')

if __name__ == '__main__':
    list = [1,2,3,4,5,6,7,8,9]
    num = 6
    location = binary_search(num,list)
    print (location)

楼主您好，刚才试了一下您回复的代码，我发现是我在给mid赋值的时候没有转成int型，但是我不明白为什么要转？

[欢乐的小猪]

def binary_search(find,array):
    low = 0
    high = len(array)-1
    while low < high:
        mid = (low + high)/2
        if find == mid:
            return mid
        elif find < mid:
            high = mid-1
        else:
            low = mid+1
 
    print('not found')
 
if __name__ == '__main__':
    list = [1,2,3,4,5,6,7,8,9]
    num = 6
    location = binary_search(num,list)
    print (location)

[欢乐的小猪]

def binary_search(find,array):
    low = 0
    high = len(array)-1
    while low <= high:
        mid = (int)((low + high)/2)
        if find == array[mid]:
            return mid
        elif find < array[mid]:
            high = mid-1
        else:
            low = mid+1

    print('not found')

if __name__ == '__main__':
    list = [1,2,3,4,5,6,7,8,9]
    num = 6
    location = binary_search(num,list)
    print (location)

[混沌鳄鱼]

import bisect
print(bisect.bisect(a=[1,2,3,4,5,6,7,8,9], x=6))

至于你的代码有什么问题，你自己看一下python36\Lib\bisect.py 中 def bisect_right 怎么写的。

[程序员的键盘]

引用 5 楼 key_1997 的回复:

[quote=引用 2 楼 hbu_pig 的回复:]

def binary_search(find,array):
    low = 0
    high = len(array)-1
    while low <= high:
        mid = (int)((low + high)/2)
        if find == array[mid]:
            return mid
        elif find < array[mid]:
            high = mid-1
        else:
            low = mid+1

    print('not found')

if __name__ == '__main__':
    list = [1,2,3,4,5,6,7,8,9]
    num = 6
    location = binary_search(num,list)
    print (location)

楼主您好，刚才试了一下您回复的代码，我发现是我在给mid赋值的时候没有转成int型，但是我不明白为什么要转？[/quote]

两个整数加起来除2是会出现小数结果的，你数组里没有小数，下标更没有小数，正常人是用下标找值的，转int是为了取整