leetcode--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 List<List<String>> partition(String s) {
		ArrayList<List<String>> res = new ArrayList<List<String>>();
		if(s.length()==0) return res;
		boolean flag[][] = new boolean[s.length()][s.length()];
		for(int i=0;i<s.length();i++){
			flag[i][i] = true;
		}
		for(int i=s.length()-1;i>=0;i--){
			for(int j=i+1;j<s.length();j++){				
				if(s.charAt(i)==s.charAt(j)){
					if(j-i==1){						
						flag[i][j] = true;
					}else{
						flag[i][j] = flag[i+1][j-1];
					}
				}else{
					flag[i][j] = false;
				}
			}
		}		
		dfs(res, flag, new ArrayList<String>(), 0, s);
		return res;
    }
    
	void dfs(ArrayList<List<String>> res,boolean[][] flag,List<String> item,int start,String s){
		if(start==flag.length){
			res.add(new ArrayList<String>(item));
		}else{
			for(int i=start+1;i<flag.length+1;i++){
				if(flag[start][i-1]){
					item.add(s.substring(start, i));
					dfs(res, flag, item, i, s);
					item.remove(item.size()-1);
				}
			}
		}
	}
}