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

Solution:
1. no "*": match char one by one.
2. "*", iterate all possible cases for "*", none, once, twice, twice,...

public class Solution {
    public boolean isMatch(String s, String p) {
        if(p.length() == 0){ 
            return s.length() == 0;
        }
        
        if(p.length() == 1 || p.charAt(1) != '*'){    // no "*" case
            if(s.length() < 1 || (p.charAt(0) != '.' && p.charAt(0) != s.charAt(0))){
                return false;
            }
            return isMatch(s.substring(1), p.substring(1));
        }
        else{
            int i = -1;
            while( i < s.length() && (i < 0 || p.charAt(0) == '.' || p.charAt(0) == s.charAt(i)) ){
                if (isMatch(s.substring(i+1), p.substring(2))){  // check cases: "*" matches zero times, once, twice, ...
                    return true;
                }
                i++; // '*' match one more time
            }
            return false;
        }
    }
}