from typing import List
import pytest
def commonPrefix(str1, str2):
    flag = 0
    if len(str1) >= len(str2):
        shorter = str2
        longer = str1
    else:
        shorter = str1
        longer = str2

    for i in range(len(shorter)):
        if shorter[i] == longer[i]:
            flag += 1
        else:
            break

    return shorter[0:flag]

def longestCommonPrefix(strs: List[str]):
    if strs == "":
        return ""
    prefix = strs[0]
    lens = len(strs)
    for i in range(1, lens):
        prefix = commonPrefix(prefix, strs[i])
        if prefix == "":
            break
    return prefix

@pytest.mark.parametrize(
    "strs, expect",
    [
        (["car", "racecar", "dog"], ""),
        (["flower", "flow", "flight"], "fl"),
        (["ba", "ca", "da"], ""),
        (["aa", ""], ""),
        (["aaa"], "aaa")
    ]
)
def test_cases(strs, expect):
    assert longestCommonPrefix(strs) == expect