[LeetCode] Regular Expression Matching(递归)

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 == '') return *s == '';  //empty

        if (*(p + 1) != '*') {//without *
            if(!matchFirst(s,p))
                return false;
            return isMatch(s + 1, p + 1);
        } else { //next: with a *
            if(isMatch(s, p + 2)) 
                return true;    //try the length of 0
            while ( matchFirst(s,p) )       //try all possible lengths 
                if (isMatch(++s, p + 2))
                    return true;
        }
    }
private:
    bool matchFirst(const char *s, const char *p){
        return (*p == *s || (*p == '.' && *s != ''));
    }
};