Time Based Key-Value Store

Design a time-based key-value data structure that can store multiple values for the same key at different time stamps and retrieve the key's value at a certain timestamp. Implement the `TimeMap` class: - `TimeMap()` Initializes the object of the data structure. - `void set(String key, String value, int timestamp)` Stores the key `key` with the value `value` at the given time `timestamp`. - `String get(String key, int timestamp)` Returns a value such that `set` was called previously, with `timestamp_prev <= timestamp`. If there are multiple such values, it returns the value associated with the largest `timestamp_prev`. If there are no values, it returns `""`.   **Example 1:** **Input** ["TimeMap", "set", "get", "get", "set", "get", "get"] [[], ["foo", "bar", 1], ["foo", 1], ["foo", 3], ["foo", "bar2", 4], ["foo", 4], ["foo", 5]] **Output** [null, null, "bar", "bar", null, "bar2", "bar2"] **Explanation** TimeMap timeMap = new TimeMap(); timeMap.set("foo", "bar", 1); // store the key "foo" and value "bar" along with timestamp = 1. timeMap.get("foo", 1); // return "bar" timeMap.get("foo", 3); // 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. timeMap.get("foo", 4); // return "bar2" timeMap.get("foo", 5); // return "bar2" ```   **Constraints:** - `1 <= key.length, value.length <= 100` - `key` and `value` consist of lowercase English letters and digits. - `1 <= timestamp <= 107` - All the timestamps `timestamp` of `set` are strictly increasing. - At most `2 * 105` calls will be made to `set` and `get`.