Regular Expression Matching

 1 public class Solution {
 2     public boolean isMatch(String s, String p) {
 3         // IMPORTANT: Please reset any member data you declared, as
 4         // the same Solution instance will be reused for each test case.
 5         if(p == null||p.length() == 0) return s == null||s.length()==0;
 6         if(p.length() < 2 || p.charAt(1) != '*')
 7         {
 8             if((s.length() > 0 && p.length() > 0 && p.charAt(0) == s.charAt(0)) || (p.charAt(0) == '.' && s.length() != 0))
 9             {
10                 return isMatch(s.substring(1), p.substring(1));
11             }
12             return false;
13         }
14         else
15         {
16             while((s.length() > 0 && p.length() > 0 && p.charAt(0) == s.charAt(0)) || (p.charAt(0) == '.' && s.length() != 0))
17             {
18                 if(isMatch(s, p.substring(2)))
19                 {
20                     return true;
21                 }
22                 s = s.substring(1);
23             }
24             return isMatch(s, p.substring(2));
25 
26         }
27     }
28 }