[LintCode] Word Break

bool wordBreak(string s, unordered_set<string> &dict) {
        int len = s.size();
        if(len == 0) return true;
        
        int min_len = INT_MAX, max_len = INT_MIN;
        for (auto &ss : dict) {
            min_len = min(min_len, (int)ss.length());
            max_len = max(max_len, (int)ss.length());
        }
        
        vector<int> breakIdx;
        breakIdx.push_back(-1);
        
        for(int i = 0;i < len;++i){
            for(int j = breakIdx.size() - 1;j >= 0;--j){
                int idx = breakIdx[j];
                if(i - idx < min_len || i - idx > max_len)
                    continue;
                string str = s.substr(idx + 1, i - idx);
                if(dict.find(str) != dict.end()){
                    breakIdx.push_back(i);
                    break;
                }
            }    
        }
        return (*breakIdx.rbegin()) == (len - 1);
    }