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).  
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

Java

http://articles.leetcode.com/2011/09/regular-expression-matching.html

public class Solution {
    public boolean isMatch(String s, String p) {
        if(p.length() == 0) {
            return s.length() == 0;
        } 
        if (p.length() == 1) {
            return s.length() == 1 && (p.charAt(0) == '.' || p.charAt(0) == s.charAt(0));
        }

        if(p.charAt(1) == '*') {
            if(isMatch(s, p.substring(2))) {
                return true;
            } else {
                return s.length() > 0 && 
                       (p.charAt(0) == '.' || p.charAt(0) == s.charAt(0)) &&
                       isMatch(s.substring(1), p);
            }
        } else {
            return s.length() > 0 &&
                   (p.charAt(0) == '.' || p.charAt(0) == s.charAt(0)) &&
                   isMatch(s.substring(1), p.substring(1));
        }
    }
}