class Solution {
public:
    bool wordBreak(string s, vector<string>& wordDict) {
        typedef unsigned long long ULL;
        const int P=131;
        unordered_set<ULL> hash;
        for(auto& word:wordDict)
        {
            ULL h=0;
            for(auto c:word)h=h*P+c;
            hash.insert(h);
        }

        int n=s.size();
        vector<bool> f(n+1);
        f[0]=true;
        s=' '+s;
        for(int i=0;i<n;i++)
        {
            if(f[i])
            {
                ULL h=0;
                for(int j=i+1;j<=n;j++)
                {
                    h=h*P+s[j];
                    if(hash.count(h))f[j]=true;
                }
            }
        }
        return f[n];
    }
};