def compare_substring(a_str, b_str):
    """ Helper for compare """
    a_digit = a_str[0].isdigit()
    b_digit = b_str[0].isdigit()
    if a_digit and not b_digit:
        return -1
    if not a_digit and b_digit:
        return 1
    if a_digit and b_digit:
        a_int = int(a_str)
        b_int = int(b_str)
        if a_int > b_int:
            return 1
        if a_int < b_int:
            return -1
    else:
        if a_str > b_str:
            return 1
        if a_str < b_str:
            return -1
    return 0
