正则表达式匹配：

Implement regular expression matching with support for'.'and'*'.

'.' Matches any single character.
'*' Matches zero or more of the preceding element.

The matching should cover the entire input string (not partial).

The function prototype should be:
bool isMatch(const char *s,const char *p)

Some examples:
isMatch("aa","a") → false
isMatch("aa","aa") → true
isMatch("aaa","aa") → false
isMatch("aa","a*") → true
isMatch("aa",".*") → true
isMatch("ab",".*") → true
isMatch("aab","c*a*b") → true

class Solution {
public:
    bool isMatch(const char *s,const char *p) {
        if(p[0] == '\0') return s[0] == '\0';
        if(p[0] == '*')  return isMatch(s,p + 1);
        if(p[1] == '*'){
            if(s[0] == '\0') return isMatch(s,p + 2);
            if(p[0] == '.')  return isMatch(s + 1,p) || isMatch(s,p + 2);
            return (s[0] == p[0] && isMatch(s + 1,p)) || isMatch(s,p + 2);
        } else {
            if(p[0] == '.')  return s[0] != '\0' && isMatch(s + 1,p + 1);
            return s[0] == p[0] && isMatch(s + 1,p + 1);
        }
    }
};