Word Break II

class Solution {
public:
    vector<string> wordBreak(string s, unordered_set<string> &dict) {
        int len = s.length();
        for(int i=0; i<len; i++){
            vector<int> tmp(len, 0);
            dp.push_back(tmp);
        }
        vector<bool> reach(len, false);
        for(int i=0; i<len; i++){
            if(i>0 && !reach[i-1]) continue;
            for(int j=i; j<len; j++){
                string sub = s.substr(i, j-i+1);
                if(dict.find(sub) != dict.end()) {
                    reach[j] = true;
                    dp[i][j] = 1;
                }
            }
        }
        string str = "";
        if(reach[len-1])
            helper(0, len, str, s);
        return ans;
    }
    
    void helper(int ind, int len, string str, string s){
        if(ind == len) {
            ans.push_back(str.substr(0, str.length()-1));
            return;
        }
        for(int i=ind; i<len; i++){
            if(dp[ind][i] == 1){
                string nstr = str + s.substr(ind, i-ind+1) + " ";
                helper(i+1, len, nstr, s);
            }
        }
    }
    
    vector<vector<int> > dp;
    vector<string> ans;
};