题目链接：https://leetcode.com/problems/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.

Example:

Input: "aab"
Output:
[
  ["aa","b"],
  ["a","a","b"]
]

class Solution {
    public List<List<String>> partition(String s) {
        List<List<String>> ans=new ArrayList();
        if(s==null||s.length()==0)
            return ans;
        helper(ans,new ArrayList<String>(),s,0);
        return ans;
    }
    public void helper(List<List<String>> ans,List<String> list,String s,int pos){
        if(pos==s.length()){
            ans.add(new ArrayList(list));
            return;
        }
        for(int i=pos;i<s.length();i++){
            if(!isPalindrome(s.substring(pos,i+1)))
                continue;
            list.add(s.substring(pos,i+1));
            helper(ans,list,s,i+1);
            list.remove(list.size()-1);
        }
    }
    public boolean isPalindrome(String s){
        if(s.length()==0)
            return false;
        if(s.length()==1)
            return true;
        int i=0,j=s.length()-1;
        while(i<j){
            if(s.charAt(i)!=s.charAt(j))
                return false;
            i++;
            j--;
        }
        return true;
    }
}