Palindrome Partitioning

Given a string s, partition s such that every substring of the partition is a palindrome.

Return all possible palindrome partitioning of s.

For example, given s = "aab",
Return

[
    ["aa","b"],
    ["a","a","b"]
  ]

 public class Solution {  
   public ArrayList<ArrayList<String>> partition(String s) {  
     ArrayList<ArrayList<String>> list = new ArrayList<ArrayList<String>>();  
     if (s == null || s.length() == 0) {  
       list.add(new ArrayList<String>());  
       return list;  
     }  
     helper(s, list, new ArrayList<String>(), 0, s.length());  
     return list;  
   }  
   public void helper(String s, ArrayList<ArrayList<String>> r, ArrayList<String> temp, int pos, int n) {  
     if (pos == n) {  
       ArrayList<String> newTemp = new ArrayList<String>(temp);  
       r.add(newTemp);  
       return;  
     }  
     // here we need an end pointer to extract each substrings  
     for (int end=pos+1; end<=n; end++) {  
       String sub = s.substring(pos, end);  
       if (isPalindrome(sub)) {  
         temp.add(sub);  
         helper(s, r, temp, end, n);  
         temp.remove(temp.size()-1);  
       }  
       // here you do not need to deal with the case that sub is not palindorme  
     }  
   }  
   public boolean isPalindrome(String string) {  
     if (string == null || string.length()==0)  
       return true;  
     boolean b = true;  
     int i=0, j=string.length()-1;  
     while (i <= j) {  
       if (string.charAt(i) != string.charAt(j))  
         b = false;  
       i++;  
       j--;  
     }  
     return b;  
   }  
 }