Day-30 Word Break II

class Solution {
    List<String> wordDict=null;
    String s=null;
    public List<String> wordBreak(String s, List<String> wordDict) {
        this.wordDict = wordDict;
        this.s = s;
        int length = s.length();
        List<String>[] result = new ArrayList[length];
        helper(0, length, result);
        return result[0];
    }
    List<String> helper(int position, int length, List<String>[] result){
        if(result[position] != null){
            return result[position];
        }
        List<String> posStr = new ArrayList<>();
        for(String w:wordDict){
            if(s.startsWith(w,position)){
                if(position + w.length() == length){
                    posStr.add(w);
                    continue;
                }
                List<String> temp = helper(position + w.length(), length, result);
                for(String r : temp){
                    posStr.add(w + " " + r);
                }
            }
        }
        result[position]=posStr;
        return posStr;
    }
}