Palindrome Partitioning

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

public class Solution {
    public List<List<String>> partition(String s) {
    	List<List<String>> res = new ArrayList<>();
    	List<String> list = new ArrayList<String>();
    	dfs(s, list, res);
    	return res;
    }
    public void dfs(String s,List<String> list,List<List<String>> res){
    	if(s.length()<1){
    		//巨大错误：！！！ 这里必须注意不能写成res.add(list); 因为后面list会改变，导致最终res里面为空
    		res.add(new ArrayList<String>(list));
    		return;
    	}
    	for(int i=0;i<s.length();i++){
    		if(IsPalindrome(0, i, s)){
    			list.add(s.substring(0,i+1));
    			dfs(s.substring(i+1), list, res);
    			list.remove(list.size()-1);
    		}
    	}
    }
    boolean IsPalindrome(int start ,int end,String s){
    	while(start<end){
    		if(s.charAt(start)==s.charAt(end)){
    			start++;
    			end--;
    		}else {
				return false;
			}
    	}
    	return true;
    }
}

public List<List<String>> partition(String s) {
        
		List<String> item = new ArrayList<String>();
        List<List<String>> res = new ArrayList<>();
        
        if(s==null||s.length()==0)
            return res;      
        dfs(s,0,item,res);
        return res;
    }
    
    public void dfs(String s, int start, List<String> item, List<List<String>> res){
        if (start == s.length()){
            res.add(new ArrayList<String>(item));
            return;
        }      
        for (int i = start; i < s.length(); i++) {
            String str = s.substring(start, i+1);
            if (isPalindrome(str)) {
                item.add(str);
                dfs(s, i+1, item, res);
                item.remove(item.size() - 1);
            }
        }
    }  
    public boolean isPalindrome(String s){
         int low = 0;
         int high = s.length()-1;
         while(low < high){
             if(s.charAt(low) != s.charAt(high))
                return false;
             low++;
             high--;
         }
         return true;
    }
}