chatgpt-palindrome.py

# https://news.ycombinator.com/item?id=38782678
import timeit, random, string, re

def is_palindrome_chatgpt_1(s):
    # [written by ChatGPT]

    # Convert the string to lowercase and remove non-alphanumeric characters
    cleaned_string = ''.join(char.lower() for char in s if char.isalnum())

    # Compare the cleaned string with its reverse
    return cleaned_string == cleaned_string[::-1]

def is_palindrome_chatgpt_1_noclean(s):
    # [manually modified from is_palindrome_chatgpt_1 to remove the cleaning/lowercase step]
    return s == s[::-1]

def is_palindrome_chatgpt_2(s):
    # [written by ChatGPT, does not clean]

    left, right = 0, len(s) - 1
    while left < right:
        if s[left] != s[right]:
            return False
        left += 1
        right -= 1
    return True


NOT_LOWERCASE_ALNUM = re.compile('[^a-z0-9]')
def is_palindrome_fast(s):
    # [written by hand]
    s = NOT_LOWERCASE_ALNUM.sub('', s.lower())
    half_length = (len(s) + 1) // 2
    return s[:half_length] == s[:-half_length-1:-1]

def is_palindrome_fast_noclean(s):
    # [modified from is_palindroem_fast to remove the cleaning/lowercase step]
    half_length = (len(s) + 1) // 2
    return s[:half_length] == s[:-half_length-1:-1]

is_palindrome_funcs = [is_palindrome_chatgpt_1, is_palindrome_chatgpt_1_noclean, is_palindrome_chatgpt_2, is_palindrome_fast, is_palindrome_fast_noclean]

alnum = string.ascii_letters + string.digits
def random_alnum(length):
    return ''.join(random.choice(alnum) for _ in range(length))


def setup():
    test_inputs = []
    for length in range(2, 5000):
        # add palindrome input
        half = random_alnum(length // 2)
        mid = random_alnum(1) if length % 2 == 1 else ''
        full = half + mid + half[::-1]
        assert len(full) == length
        assert all(is_palindrome(full) for is_palindrome in is_palindrome_funcs)
        test_inputs.append(full)

        # add almost-palindrome input
        possible_change_positions = list(range(length))
        if length % 2 == 1:
            possible_change_positions.remove(length // 2)
        change_pos = random.choice(possible_change_positions)
        new_char = 'a' if full[change_pos] not in 'Aa' else 'b'
        full = full[:change_pos] + new_char + full[change_pos + 1:]
        assert len(full) == length
        assert not any(is_palindrome(full) for is_palindrome in is_palindrome_funcs)
        test_inputs.append(full)
    return test_inputs

def go():
    test_inputs = setup()
    for func in is_palindrome_funcs:
        print(func, timeit.timeit(lambda: sum(func(inp) for inp in test_inputs), number=1))
go()