LeetCode - Palindrome Partitioning

Palindrome Partitioning

public ArrayList<ArrayList<String>> partition(String s) {
        ArrayList<ArrayList<String>> ret = new ArrayList<ArrayList<String>>();
        if(s == null || s.length()==0) return ret;
        helper(ret, s, new ArrayList<String>());
        return ret;
    }
    
    public void helper(ArrayList<ArrayList<String>> ret, String s, ArrayList<String> lst){
        if(s.length() == 0){
            ret.add(new ArrayList<String>(lst));
            return;
        }
        
        for(int i=1; i <= s.length(); i++){  // don't forget to consider "=" case
            String cur = s.substring(0, i);
            if(IsPalindrome(cur)){
                lst.add(cur);
                helper(ret, s.substring(i), lst);
                lst.remove(lst.size()-1);
            }
        }
    }
    
    public boolean IsPalindrome(String str){
        if(str == null || str.length() == 0) return false;
        int left = 0, right = str.length() - 1;
        while(left < right){
            if(str.charAt(left) != str.charAt(right)){
                return false;
            }
            left++;
            right--;
        }
        return true;
    }