python 正则的使用例子和goupby

111122333类似这字符串的分类

Solution 1 ... using a regular expression
def countAndSay(self, n):
    s = ''
    for _ in range(n - 1):
        s = re.sub(r'(.)\1*', lambda m: str(len(m.group(0))) + m.group(1), s)
    return s

Solution 2 ... using a regular expression
def countAndSay(self, n):
    s = ''
    for _ in range(n - 1):
        s = ''.join(str(len(group)) + digit
                    for group, digit in re.findall(r'((.)\2*)', s))
    return s

Solution 3 ... using groupby
def countAndSay(self, n):
    s = ''
    for _ in range(n - 1):
        s = ''.join(str(len(list(group))) + digit
                    for digit, group in itertools.groupby(s))
    return s