Design Underground System LeetCode solution in C++

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typedef pair<string, int> PSI;
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typedef pair<string, string> PSS;
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typedef vector<int> VI;
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typedef vector<PSI> VPSI;
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typedef map<PSS, VI> HPSSVI;
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typedef map<int, VPSI> HIVPSI;
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class UndergroundSystem {
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  HPSSVI schedule;
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  HIVPSI customer;
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 public:
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  UndergroundSystem() {}
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  void checkIn(int id, string stationName, int t) {
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    customer[id].push_back(make_pair(stationName, t));
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  }
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  void checkOut(int id, string stationName, int t) {
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    auto it = customer.find(id);
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    int idx = it->second.size() - 1;
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    schedule[{it->second[idx].first, stationName}].push_back(t - it->second[idx].second);
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  }
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  double getAverageTime(string startStation, string endStation) {
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    double sum = 0.0;
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    int s = schedule[{startStation, endStation}].size();
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    auto it = schedule.find({startStation, endStation});
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    for (int i = 0; i < s; i++) sum += schedule[{startStation, endStation}][i];
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    return sum / s;
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  }
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};
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/**
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 * Your UndergroundSystem object will be instantiated and called as such:
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 * UndergroundSystem* obj = new UndergroundSystem();
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 * obj->checkIn(id,stationName,t);
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 * obj->checkOut(id,stationName,t);
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 * double param_3 = obj->getAverageTime(startStation,endStation);
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 */