Time Based Key-Value Store

Time Based Key-Value Store is a Medium Data Structures and Algorithms interview problem you can solve, run and submit on Thita.ai. It belongs to the Design Patterns pattern, in the Design (General/Specific) subpattern.

Problem statement

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 timestampprev <= timestamp. If there are multiple such values, it returns the value associated with the largest timestampprev. 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.

Topics and companies

Topics: Hash Table, String, Binary Search, Design.

Reported in interviews at Oracle, ByteDance, Uber, Apple, Lyft, Sumologic, Google, Atlassian, Microsoft, Twitter, Netflix.

How to practise Time Based Key-Value Store on Thita.ai

Starter code is provided in C, C#, C++, Go, Java, JavaScript and Python. Your solution runs against 5 test cases for this problem, with the AI coach available for a hint when you are stuck rather than a finished answer. The reference solution runs in O(1) for set, O(log N) for get (where N is the number of set operations for a given key). set is O(1) due to push_back, get uses binary search over the vector for the key. time and O(K + Q), where K is the number of unique keys and Q is the total number of set operations (since each set stores a value and timestamp). space.

Open Time Based Key-Value Store in the code editor, or read the Time Based Key-Value Store editorial for a worked solution with its approach and complexity analysis.

Where Time Based Key-Value Store sits in the DSA pattern sheet

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