Merge pull request #2703 from leahjia/1396-design-underground-system

create 1396-design-underground-system.java

Author: felivalencia3

java/1396-design-underground-system.java

@@ -0,0 +1,41 @@
+class UndergroundSystem {
+    // id, src, time
+    Map<Integer, Pair<String, Integer>> entries;
+    // src, dest, int[total time, number of travels]
+    Map<String, Map<String, int[]>> times;
+
+    public UndergroundSystem() {
+        this.entries = new HashMap<>();
+        this.times = new HashMap<>();
+    }
+    
+    public void checkIn(int id, String stationName, int t) {
+        entries.put(id, new Pair<>(stationName, t));
+    }
+    
+    public void checkOut(int id, String dest, int t) {
+        Pair<String, Integer> entry = entries.get(id);
+        String src = entry.getKey();
+        int duration = t - entry.getValue();
+
+        Map<String, int[]> city = times.getOrDefault(src, new HashMap<>());
+        int[] total = city.getOrDefault(dest, new int[2]);
+        total[0] += duration;
+        total[1]++;
+        city.put(dest, total);
+        times.put(src, city);
+    }
+    
+    public double getAverageTime(String startStation, String endStation) {
+        int[] total = times.get(startStation).get(endStation);
+        return 1.0 * total[0] / total[1];
+    }
+}
+
+/**
+ * Your UndergroundSystem object will be instantiated and called as such:
+ * UndergroundSystem obj = new UndergroundSystem();
+ * obj.checkIn(id,stationName,t);
+ * obj.checkOut(id,stationName,t);
+ * double param_3 = obj.getAverageTime(startStation,endStation);
+ */