LeetCode: Word Break II

难题

class Solution {
public:
    void dfs(string s, vector<string> &tmp, vector<string> &res, unordered_set<string> &unused, unordered_set<string> &dict) {
        if (s.size() == 0) {
            string ans = "";
            for (int i = 0; i < tmp.size(); i++) {
                if (i == 0) ans += tmp[i];
                else ans += " " + tmp[i];
            }
            res.push_back(ans);
            return;
        }
        if (unused.find(s) != unused.end()) return;
        int pre = res.size();
        for (int i = 1; i <= s.size(); i++) {
            if (dict.find(s.substr(0, i)) != dict.end()) {
                tmp.push_back(s.substr(0, i));
                dfs(s.substr(i, s.size()-i), tmp, res, unused, dict);
                tmp.pop_back();
            }
        }
        if (res.size() == pre) unused.insert(s);
    }
    vector<string> wordBreak(string s, unordered_set<string> &dict) {
        vector<string> res;
        unordered_set<string> unused;
        vector<string> tmp;
        dfs(s, tmp, res, unused, dict);
        return res;
    }
};

 C#

public class Solution {
    public List<string> WordBreak(string s, ISet<string> wordDict) {
        List<string> ans = new List<string>();
        HashSet<string> unused = new HashSet<string>();
        List<string> tmp = new List<string>();
        dfs(s, ref tmp, ref ans, ref unused, wordDict);
        return ans;
    }
    public void dfs(string s, ref List<string> tmp, ref List<string> ans, ref HashSet<string> unused, ISet<string> wordDict) {
        if (s.Length == 0) {
            string res = "";
            for (int i = 0; i < tmp.Count; i++) {
                if (i == 0) res += tmp[i];
                else res += " " + tmp[i];
            }
            ans.Add(res);
            return;
        }
        if (unused.Contains(s) == true) return;
        int pre = ans.Count;
        for (int i = 1; i <= s.Length; i++) {
            if (wordDict.Contains(s.Substring(0, i))) {
                tmp.Add(s.Substring(0, i));
                dfs(s.Substring(i, s.Length-i), ref tmp, ref ans, ref unused, wordDict);
                tmp.RemoveAt(tmp.Count-1);
            }
        }
        if (ans.Count == pre) unused.Add(s);
    }
}