Regular Expression Matching

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

public class Solution {
    public boolean isMatch(String s, String p) {
    	if (s == null || p == null) {
    		return false;
    	}
        return process(s, p, 0, 0);
    }

	private boolean process(String s, String p, int si, int pi) {
		// TODO Auto-generated method stub
		if (pi == p.length()) {  
			return si == s.length();
		}
		if (pi + 1 == p.length() || p.charAt(pi + 1) != '*') {
			return si != s.length() && (s.charAt(si)==p.charAt(pi) || p.charAt(pi) == '.')
					&& process(s, p, si+1, pi+1);
		}
		while (si != s.length() && (s.charAt(si)==p.charAt(pi) || p.charAt(pi) == '.')) {
			if (process(s, p, si, pi+2)) {
				return true;
			}
			si++;
		}
		return process(s, p, si, pi+2);
	}
}