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LeetCode: Word Break II

Posted on Edited on In , Valine: 
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class Solution {
public:
    vector<string> wordBreak(string s, unordered_set<string>& wordDict) {
        unordered_map<string, vector<string>> map;
        return foo(s, wordDict, map);
    }

    vector<string> foo(string s, unordered_set<string> &wordDict, unordered_map<string, vector<string>> &map)
    {
        if(map.find(s)!=map.end())
        {
            return map[s];
        }

        vector<string> res;
        if(s.length()==0)
        {
            res.push_back("");
            return res;
        }

        for(string word: wordDict)
        {
            if(startsWith(s, word))
            {
                auto subList=foo(s.substr(word.length()), wordDict, map);
                for(auto sub: subList)
                    res.push_back(word+(sub.size()==0?"":" ")+sub);
            }
        }
        map[s]=res;
        return res;
    }

    bool startsWith(string lhs, string rhs)
    {
        if(lhs.length()<rhs.length())
            return false;
        for(int i=0;i<rhs.length(); ++i)
            if(lhs[i]!=rhs[i])
                return false;
        return true;
    }
};