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Grokking the Coding Interview Patterns in JavaScript

Time Based Key-Value Store

Explore how to implement a custom data structure that stores multiple values for the same key at different timestamps. Learn to retrieve the correct value given a timestamp, handling cases where exact matches are unavailable, using JavaScript.

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Statement

Implement a data structure that can store multiple values of the same key at different timestamps and retrieve the key’s value at a certain timestamp.

You’ll need to implement the TimeStamp class. This class has the following functions:

  • Init(): This function initializes the values dictionary and timestamp dictionary.

  • Set Value(key, value, timestamp): This function stores the key and value at any given timestamp.

  • Get Value(key, timestamp): This function returns the value set for this key at the specified timestamp.

Note: When a query requests the value of a key at a timestamp that isn’t recorded, return the value corresponding to the most recent timestamp before the query’s timestamp. If there are no timestamps before the query’s timestamp, return an empty string.

Constraints:

  • 1≤1 \leq key.length, value.length ≤20\leq 20
  • key and value consist of lowercase English letters and digits.
  • 1≤1 \leq timestamp ≤103\leq 10^3
  • At most 1×1031 \times 10^3 calls will be made to Set Value and Get Value.
  • All the timestamps, timestamp, of Set Value are strictly increasing.

Examples

Understand the problem

Let’s take a moment to make sure you’ve correctly understood the problem. The quiz below helps us to check that you’re solving the correct problem:

Time-Based Key-Value Store

1.

Given this series of commands, what is the output of the last command?

Init()

Set Value(“prediction”, “winning”, 3)

Get Value(“prediction”, 2)

A.

“winning”

B.

“losing”

C.

“”

1 / 3

Figure it out!

We have a game for you to play. Rearrange the logical building blocks required to implement Get Value().

Sequence - Vertical
Drag and drop the cards to rearrange them in the correct sequence.
1
2
3
4

Try it yourself

Implement your solution in the following coding playground.

JavaScript
usercode > time_stamp.js
class TimeStamp {
    constructor() {
        this.valuesDict = {};
        this.timestampsDict = {};
    }
    // Set TimeStamp data variables
    setValue(key, value, timestamp) {
        // Write your code here
    }
    // Get time_stamp data variables
    getValue(key, timestamp) {
        // Write your code here
    }
}
export default TimeStamp
Time Based Key-Value Store