day 42: 981-time-based-key-value-store

981-time-based-key-value-store/driver.cpp

@@ -0,0 +1,13 @@
+#include "soln.cpp"
+
+int main()
+{
+	TimeMap timeMap;
+	timeMap.set("foo", "bar", 1);		   // store the key "foo" and value "bar" along with timestamp = 1.
+	cout << timeMap.get("foo", 1) << endl; // return "bar"
+	cout << timeMap.get("foo", 3) << endl; // return "bar", since there is no value corresponding to foo at timestamp 3 and timestamp 2, then the only value is at timestamp 1 is "bar".
+	timeMap.set("foo", "bar2", 4);		   // store the key "foo" and value "bar2" along with timestamp = 4.
+	cout << timeMap.get("foo", 4) << endl; // return "bar2"
+	cout << timeMap.get("foo", 5) << endl; // return "bar2"
+	return 0;
+}

981-time-based-key-value-store/soln.cpp

@@ -0,0 +1,51 @@
+#include <bits/stdc++.h>
+using namespace std;
+class TimeMap
+{
+public:
+	unordered_map<string, vector<pair<int, string>>> timemap;
+	TimeMap()
+	{
+	}
+
+	void set(string key, string value, int timestamp)
+	{
+		timemap[key].push_back({timestamp, value});
+	}
+
+	string get(string key, int timestamp)
+	{
+		if (timemap.find(key) == timemap.end())
+		{
+			return "";
+		}
+		else if (timemap[key].size() == 1)
+		{
+			return timemap[key][0].first <= timestamp ? timemap[key][0].second : "";
+		}
+		// binary search
+		int low = 0, high = timemap[key].size(), mid;
+		while (low < high)
+		{
+			mid = low + (high - low) / 2;
+			if (timemap[key][mid].first <= timestamp)
+			{
+				low = mid + 1;
+			}
+			else
+			{
+				high = mid;
+			}
+		}
+		// Now, low points to the element that succeeds the given timestamp
+		// so we want the one before it
+		return low > 0 && low <= timemap[key].size() ? timemap[key][low - 1].second : "";
+	}
+};
+
+/**
+ * Your TimeMap object will be instantiated and called as such:
+ * TimeMap* obj = new TimeMap();
+ * obj->set(key,value,timestamp);
+ * string param_2 = obj->get(key,timestamp);
+ */