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class Codec {
public:

    // Encodes a list of strings to a single string.
    string encode(vector<string>& strs) {
        string encoded = "";
        for (string &str: strs) {
            int len = str.size();
            encoded += to_string(len) + "@" + str;
        }
        return encoded;
    }

    // Decodes a single string to a list of strings.
    vector<string> decode(string s) {
        vector<string> r;
        int head = 0;
        while(head < s.size()) {
            int at_pos = s.find('@', head);
            int len = stoi(s.substr(head, at_pos - head));
            head = at_pos + 1;
            r.push_back(s.substr(head, len));
            head += len;
        }
        return r;
    }
};


// Your Codec object will be instantiated and called as such:
// Codec codec;
// codec.decode(codec.encode(strs));