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) {
		// Note: The Solution object is instantiated only once and is reused by each test case.    
		if(s == NULL || p == NULL)return false;

		// special cases
		if(*p == '\0')return *s == '\0';

		// the next character is not '*'
		if(*(p+1) != '*'){
			return (*s == *p || (*p == '.' && *s != '\0')) && isMatch(s+1, p+1);
		}

		// the next character is '*'
		while(*s != '\0' && (*s == *p || *p == '.')){
			if(isMatch(s, p+2)){
				return true;
			}
			s++;
		}
		return isMatch(s, p+2);
	}
};