LeetCode Word Break II

class Solution {
private:
    vector<string> result;
public:
    vector<string> wordBreak(string s, unordered_set<string> &dict) {
        vector<vector<int> > dp;
        result.clear();
        
        int len = s.length();
        dp.resize(len + 1);
        dp[0].push_back(-1);
        
        for (int i=1; i<=len; i++) {
            for (int j=i-1; j>=0; j--) {
                string str = s.substr(j, i - j);
                if (dict.find(str) != dict.end()) {
                    if (dp[j].empty()) continue;
                    dp[i].push_back(j);
                }
            }
        }
        dfs_build(dp, s, len, "");
        return result;
    }
    
    void dfs_build(vector<vector<int> >& dp, string& s, int len, string sent) {
        vector<int> indices = dp[len];
        for (int i=0; i<indices.size(); i++) {
            int prefix_len = indices[i];
            if (prefix_len <= 0) {
                result.push_back(s.substr(0, len) + sent);
            } else {
                string suffix = s.substr(prefix_len, len - prefix_len);
                dfs_build(dp, s, prefix_len, " " + suffix + sent);
            }
        }
    }
};

class Solution {
public:
    vector<string> wordBreak(string s, unordered_set<string> &dict) {
        vector<vector<string> > dp;
        int len = s.length();
        dp.resize(len + 1);
        dp[0].push_back("");
        
        for (int i=1; i<=len; i++) {
            for (int j=i-1; j>=0; j--) {
                string str = s.substr(j, i - j);
                if (dict.find(str) != dict.end()) {
                    vector<string>& prefix = dp[j];
                    if (prefix.empty()) continue;
                    for (int k=0; k<prefix.size(); k++) {
                        if (prefix[k].length() == 0) {
                            dp[i].push_back(str);
                        } else {
                            dp[i].push_back(prefix[k] + " " + str);
                        }
                    }
                }
            }
        }
        vector<string> ret = dp[len];
        dp.clear();
        return ret;
    }
};