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Problem · Hash Table

In-Memory Database with TTL

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AutodeskFULLTIMEOA

Problem statement

Process a finite batch of timestamped operations on an in-memory key-value database. Timestamps are nondecreasing, and rows with the same timestamp are processed in input order. An entry set at time t with TTL d is active while now < t + d.

Operation	Returned string
`["SET", key, value, ttl, now]`	Store the value and expiration. Return `true` if the key had an active value immediately before this operation, otherwise `false`.
`["GET", key, now]`	Return the active value, or `NULL`.
`["COUNT", now]`	Return the number of active keys.

Expired entries do not count as existing and may be removed lazily.

Function

runTimedDatabase(operations: String[][]) → String[]

Examples

Example 1

operations = [["SET","a","1","5","0"],["GET","a","4"],["GET","a","5"],["COUNT","5"]]return = ["false","1","NULL","0"]

Key a is active before time 5 and expires exactly at time 5.

Example 2

operations = [["SET","x","old","10","1"],["SET","x","new","3","4"],["GET","x","6"],["SET","x","fresh","5","7"],["COUNT","7"]]return = ["false","true","new","false","1"]

The first overwrite finds x active. The second value expires at time 7, so the next set reports false and creates a fresh active entry.

Constraints

1 <= operations.length <= 200000.
Keys and values are non-empty ASCII strings and values are never NULL.
Timestamps are nondecreasing integers from 0 through 10^18.
Every TTL is an integer from 1 through 10^18.