def spellCheck(lookupWord: str, words: str) -> str | None:
    """Spell check a word against a list of words."""
    map = {}
    for word in words.split():
        map[word] = levenshtein(lookupWord, word)
    min_distance = min(map.values())
    if min_distance >= 3:
        return None
    return ",".join([word for word in map.keys() if map[word] == min_distance])


# from: https://en.wikibooks.org/wiki/Algorithm_Implementation/Strings/Levenshtein_distance#Python
def levenshtein(s1: str, s2: str) -> int:
    if len(s1) < len(s2):
        return levenshtein(s2, s1)

    # len(s1) >= len(s2)
    if len(s2) == 0:
        return len(s1)

    previous_row = range(len(s2) + 1)
    for i, c1 in enumerate(s1):
        current_row = [i + 1]
        for j, c2 in enumerate(s2):
            insertions = (
                previous_row[j + 1] + 1
            )  # j+1 instead of j since previous_row and current_row are one character longer
            deletions = current_row[j] + 1  # than s2
            substitutions = previous_row[j] + (c1 != c2)
            current_row.append(min(insertions, deletions, substitutions))
        previous_row = current_row

    return previous_row[-1]


print("Testing spellCheck()...", end="")
words = "cat cow dog frog"
assert spellCheck("frog", words) == "frog"  # frog is correct
assert spellCheck("cats", words) == "cat"  # cat is distance 1
assert spellCheck("caw", words) == "cat,cow"  # cat and cow are distance 1
assert spellCheck("drog", words) == "dog,frog"  # dog and frog are distance 1
assert spellCheck("kit", words) == "cat"  # cat is distance 2
assert spellCheck("ack", words) == None  # cat, cow, and dog are
# distance 3 (too far)
print("Passed!")