天题系列：Regular Expression Matching

烧脑神题

public class Solution {

    public boolean isMatch(String s, String p) {

        // 反正我是想不出来 http://www.cnblogs.com/springfor/p/3893593.html

        if(p.length()==0) return s.length()==0;

        if(p.length()==1) return (s.length()==1 &&(p.charAt(0)==s.charAt(0)||p.charAt(0)=='.'));

        

        if(p.charAt(1)!='*'){

            if(s.length()<1) return false;   

            

            return (s.charAt(0)==p.charAt(0)||p.charAt(0)=='.')&&(isMatch(s.substring(1), p.substring(1)));

        }else{

            while(s.length()>0&&(p.charAt(0)==s.charAt(0)||p.charAt(0)=='.')){

                if(isMatch(s , p.substring(2)))

                    return true;

                s = s.substring(1); // p= a*????; s = aaaaa????

            }

            return isMatch(s, p.substring(2)); // p= b*?????, s = a????

        }

        

    }

}