Leetcode(java) 140. Word Break II

Q:

Given a string s and a dictionary of strings wordDict, add spaces in s to construct a sentence where each word is a valid dictionary word. Return all such possible sentences in any order.

Note that the same word in the dictionary may be reused multiple times in the segmentation.

Example 1:

Input: s = "catsanddog", wordDict = ["cat","cats","and","sand","dog"]
Output: ["cats and dog","cat sand dog"]

A:  To solve this problem, we need record every result of match, dynamic programming can not complete it. Therefore, I use DFS to search all possible answers and record every result.

class Solution {
    public List<String> wordBreak(String s, List<String> wordDict) {
        ans = new ArrayList<>();
        res = new ArrayList<>();
        dfs(s,wordDict,0);

        return ans;

    }

    void dfs(String s, List<String> wordDict, int start) {
        if(start>=s.length()){
            ans.add(new String(String.join(" ",res)));
        }else{
            for(String w:wordDict){
                int end = start + w.length();
                if(end<=s.length() && w.equals(s.substring(start,end))){
                    res.add(w);
                    dfs(s,wordDict,end);
                    res.remove(res.size()-1);
                }
            }
        }


    }



     List<String> ans;
     List<String> res;
}