Create design-underground-system.cpp

Author: kamyu104

C++/design-underground-system.cpp

@@ -0,0 +1,28 @@
+// Time:  O(n)
+// Space: O(n)
+
+class UndergroundSystem {
+public:
+    UndergroundSystem() {
+        
+    }
+    
+    void checkIn(int id, string stationName, int t) {
+        live_[id] = {stationName, t};
+    }
+    
+    void checkOut(int id, string stationName, int t) {
+        const auto [startStation, startTime] = move(live_[id]); live_.erase(id);
+        statistics_[startStation][stationName].first += t - startTime;
+        ++statistics_[startStation][stationName].second;
+    }
+    
+    double getAverageTime(string startStation, string endStation) {
+        const auto& [numer, denom] = statistics_[startStation][endStation];
+        return double(numer) / denom; 
+    }
+
+private:
+    unordered_map<int, pair<string, int>> live_;
+    unordered_map<string, unordered_map<string, pair<int, int>>> statistics_;
+};