981 - Time Based Key-Value Store.

Medium

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.

• <code>1 <= timestamp <= 10⁷</code>

• All the timestamps timestamp of set are strictly increasing.

• At most <code>2 * 10⁵</code> calls will be made to set and get.