二分法查找 python实现

写了两种常见的实现

二分法查找：从有序集合a中找到具体值b所在位置
a = [1,2,3,4,5,6,7,8,9]
b = 2

1. 通过while循环实现二分查找

def ef1(a,b):
    a_len = len(a)
    begin = 0
    end = a_len
    index = int(a_len/2)
    deep = 0
    while True:
        deep = deep+1
        print(deep,end='')
        if b==a[index]:
            print('\nfind b on index={},b={},find={}'.format(index,b,a[index]))
            break
        elif a[index] > b:
            end = index-1
        else:
            begin = index+1
        index = int((end+begin)/2)
a = range(100)
for b in range(100) :
    ef1(a,b)
>>>
123456
find b on index=0,b=0,find=0
...
1
find b on index=50,b=50,find=50
...
123456
find b on index=99,b=99,find=99

2. 通过函数嵌套实现，运行结果同上

def erf(a,b,begin,end,deep=0):
    deep = deep+1
    print(deep,end='')
    index = int((begin+end)/2)
    if b==a[index]:
        print('\nfind b on index={},b={},find={}'.format(index,b,a[index]))
    elif a[index] > b:
        end = index-1
        erf(a,b,begin,end,deep)
    else:
        begin = index+1
        erf(a,b,begin,end,deep)


a = range(100)
begin = 0
end = len(a)

for b in a:
    erf(a,b,begin,end)