Word Break II

Given a string s and a dictionary of words dict, add spaces in s to construct a sentence where each word is a valid dictionary word.

Return all such possible sentences.

For example, given
s = "catsanddog",
dict = ["cat", "cats", "and", "sand", "dog"].

A solution is ["cats and dog", "cat sand dog"].

public class Solution {
    public ArrayList<String> wordBreak(String s, Set<String> dict) {
        ArrayList<String>  res = new ArrayList<String> ();
        if(s.length()<=0) return res;
        StringBuilder sb = new StringBuilder();
        DFS(s,dict,new boolean[s.length()+1],0,sb,res);
        return res;
    }
    public void DFS(String s,Set<String> dict,boolean[]p,int start, StringBuilder output,ArrayList<String>res){
        if(s.length()==start){
            String temp = output.toString();
            temp = temp.substring(0,temp.length()-1);
            res.add(temp);
            return;
        }
        for(int i=start;i<s.length();i++){
            String piece = s.substring(start,i+1);
            if(dict.contains(piece) && !p[i+1]){
                output.append(piece);
                output.append(" ");
                int curSize = res.size();
                DFS(s,dict,p,i+1,output,res);
                if(res.size()==curSize)
                    p[i+1] = true;
                int end = output.length();
                int begin = end - piece.length()-1;
                output.delete(begin,end);
            }
        }
    }
}

 res.add(sb.toString().substring(0,sb.length()-1));

int begin = end -pieces.length()-1;