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"].

dfs超时

public class Solution {    public List<String> wordBreak(String s, Set<String> dict) {       LinkedList<String> res=new LinkedList<String>();       LinkedList<String> path=new LinkedList<String>();       if(s==null || dict==null || dict.size()==0) return res;              int n=s.length();       boolean []f=new boolean[n+1];       boolean [][]prev=new boolean[n+1][n];       f[0]=true;       //dp       for(int i=1;i<=n;i++){           for(int j=i-1;j>=0;j--){               if( f[j] && dict.contains( s.substring(j,i) ) ){                   f[i]=true;                   prev[i][j]=true;               }           }       }       getPath(s.length(),s,prev,res,path);       return res;    }    //dfs    public void getPath(int curr,String s, boolean [][]prev,LinkedList<String> res,LinkedList<String> path){        if(curr==0){            StringBuilder sb=new StringBuilder();            for(String ss : path){                sb.append(ss);                sb.append(" ");            }            res.add(sb.toString().trim());        }        for(int i=0;i<curr;i++){            if(prev[curr][i]){                path.addFirst(s.substring(i,curr));                getPath(i,s,prev,res,path);                path.pollFirst();            }        }    }}