LeetCode Word Break II DP+DFS

class Solution {
public:
    void dfs(vector<string> &ans, string &s, unordered_set<string> &wordDict, string str, int idx, vector<bool> &dp) {
        string substr;
        for(int len = 1; idx + len <= s.length(); ++len) {
            if(dp[idx + len] && wordDict.count(s.substr(idx, len)) == 1) {
                substr = s.substr(idx, len);
                if(idx + len < s.length()) {
                    dfs(ans, s, wordDict, str + substr + " ", idx + len, dp);
                }else {
                    ans.push_back(str + substr);
                    return;
                }
            }
        }
    }
    vector<string> wordBreak(string s, unordered_set<string>& wordDict) {
        vector<string> ans;
        if(wordDict.size() == 0) return ans;
        vector<bool> dp(s.size() + 1, false);
        dp[0] = true;
        //判断是否可以切分
        for(int i = 1; i <= s.size(); ++i) {
            for(int j = i - 1; j >= 0; --j) {
                if(dp[j]) {
                    string temp = s.substr(j, i - j);
                    if(wordDict.find(temp) != wordDict.end()) {
                        dp[i] = true;
                        break;
                    }
                }
            }
        }
        //如果可以切分，DFS去切分
        if(dp[s.size()]) {
            dfs(ans, s, wordDict, "", 0, dp);
        }
        return ans;
    }
};