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Regular Expression Matching

10. 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 (p.length() == 0) {
            return s.length() == 0;
        }

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

            int i = 0;
            while (i < s.length() && (s.charAt(i) == p.charAt(0) || p.charAt(0) == '.')) {
                if (isMatch(s.substring(i + 1), p.substring(2))) {
                    return true;
                }
                i++;
            }

            return false;
        }
    }
}

Hope this helps,
Michael