python 3.6 中的二进制搜索

Question

I am writing a binary search function for a school assignment and while it works fine for my own tests, checking it in the upload submission portal returns that it fails the majority of hidden tests. Is there anything obviously wrong with it, ie the assignment for left, right, middle being incorrect etc? (other than it being very crude)

EDIT: added more details that were missing, yes the list in stolen_plates will be sorted. The test I have at the bottom works fine for me but there must be something I am overlooking for it to fail the submission tests

def binary_simple_plate_finder(stolen_plates, sighted_plates):

    result_list = []
    
    total_comparisons = 0
    for plate in sighted_plates:
        middle = (len(stolen_plates) - 1) // 2
        right = (len(stolen_plates) - 1)
        left = 0
        finished = False
        while not finished:
            if plate == stolen_plates[middle]:
                total_comparisons = total_comparisons + 1
                result_list.append(plate)
                finished = True
            elif left == right and plate != stolen_plates[middle]:
                total_comparisons = total_comparisons + 1
                finished = True            
            elif plate > stolen_plates[middle]:
                total_comparisons = total_comparisons + 1
                left = middle + 1
                middle = ((left + right) // 2)
            elif plate < stolen_plates[middle]:
                total_comparisons = total_comparisons + 1
                right = middle - 1
                middle = ((left + right) // 2)
            
    return result_list, total_comparisons

stolen = ["ABJ603", "BADMON", "CHUD69", "CRAP22", "DENGEL", "EFFETE", "IMGAY", "NINGAS", "OKEDOK", "PUS556", "ZMAN21"]
sighted = ["OKEDOK", "ABJ603", "BASTAR", "NINGAS"]
print(binary_simple_plate_finder(stolen, sighted))

Answer 1

Here's a binary search implementation that also counts the number of comparisons.

You'll need to populate sighted_plates and stolen_plates and remember that stolen_plates needs to be sorted.

def bsearch(lst, x):
    c = 0
    L = 0
    R = len(lst) - 1
    while L <= R:
        m = (L + R) // 2
        c += 1
        if (v := lst[m]) == x:
            return m, c
        c += 1
        if v < x:
            L = m + 1
        else:
            R = m - 1
    return -1, c

stolen_plates = sorted(["ABJ603", "BADMON", "CHUD69", "CRAP22", "DENGEL", "EFFETE", "IMGAY", "NINGAS", "OKEDOK", "PUS556", "ZMAN21"])

sighted_plates = ["OKEDOK", "ABJ603", "BASTAR", "NINGAS"]

result_list = [] # list of stolen plates that have been sighted

total_comparisons = 0

for plate in sighted_plates:
    i, c = bsearch(stolen_plates, plate)
    if i >= 0:
        result_list.append(plate)
    total_comparisons += c

print(*result_list, sep='\n')
print(f'{total_comparisons=}')

Output:

OKEDOK
ABJ603
NINGAS
total_comparisons=23