Log for 電訊台

    string destCity(vector<vector<string>>& paths) {
        unordered_map<string, string> adj;
        for (auto &x : paths) adj[x[0]] = x[1];
        auto &x = adj.begin()->second;
        while (adj.find(x) != adj.end()) x = adj[x];
        return x;
    }