简单模拟正则表达式匹配字符串

输入字符串s，p，p中可能包含字符"."和"*"：使用正则表达式的规则判断s和p是否匹配

示例：

　　输入：s="abc" p =".*c"

　　输出：True

Python解决方案：

class Solution(object):
    def isMatch(self, s, p):
        """
        :type s: str
        :type p: str
        :rtype: bool
        """
        len_p = len(p)
        len_s = len(s)
        if len_p == 0:
            return len_s == 0
        judge = len_s > 0 and p[0] in [".",s[0]]
        if len_p > 1 and p[1] == "*":
            if judge:
                return self.isMatch(s[1:],p) or self.isMatch(s,p[2:])
            else:
                return self.isMatch(s,p[2:])
        else:
            return judge and self.isMatch(s[1:],p[1:])

改进方案（转自leetcode用csler）：

class Solution:
    def __init__(self):
        self.cache = {}
    def isMatch(self, s: 'str', p: 'str') -> 'bool':
        if len(p) == 0:     return len(s) == 0
        question = s + '+' + p
        if question in self.cache:
            return self.cache[question]
        firstMatch = len(s) > 0 and (p[0] == s[0] or p[0] == '.')
        if len(p) > 1 and p[1] == '*':
            if firstMatch:
                res = self.isMatch(s[1:], p) or self.isMatch(s, p[2:])
            else:
                res = self.isMatch(s, p[2:])
        else:
            res = firstMatch and self.isMatch(s[1:], p[1:])
        self.cache[question] = res
        return res