该函数不会遍历整个数组

Question

I have the following code which gets two arrays and finds the location of each item in the second array based on the first array. For example, for 23 from loc1 , which is between 20 and 25 in array it should return 20.

matrix_x = []
def binarySearch(alist, loc):
    for item in loc:
        midpoint = len(alist)//2
        if midpoint == 1:
            if item<alist[midpoint]:
                return matrix_x.append(alist[midpoint-1])
            else:
                return matrix_x.append(alist[midpoint])         
        else:
            if item<alist[midpoint]:
                return binarySearch(alist[:midpoint],loc)
            else:
                return binarySearch(alist[midpoint:],loc)
    return matrix_x

array = [5,10,15,20,25]
loc1= [23,7,11]

print(binarySearch(array, loc1))
print(matrix_x)

I expect to receive this array as the result:

[20,5,10]

But I receive only the first item like this:

[20]

Answer 1

You're returning the matrix_x.append statement, so it only ever appends 1 item, in this case 20 . To get the behavior you want, you may need to restructure your function some.

Answer 2

Just use the bisect module :

import bisect

def binarySearch(alist, loc):
    return [alist[bisect.bisect(alist, i) - 1] for i in loc]

array = [5,10,15,20,25]
loc1= [23,7,11]
print(binarySearch(array, loc1))

Output:

[20, 5, 10]

Finding the index is simpler:

def binarySearchIndex(alist, loc):
    return [bisect.bisect(alist, i) - 1 for i in loc]