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In-Memory Database with Permanent and Expiring Values

Klaviyo● MediumFULLTIMEOA

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Problem statement

Implement an in-memory key-value database with permanent and time-limited writes. Process the given operations in order and return one string result for each operation.

Operations

["SET", time, key, value]: store value under key without an expiration time. Replace any earlier value and deadline. Return "".
["SET_TTL", time, key, value, ttl]: store value under key with expiration time time + ttl. Replace any earlier value and deadline. Return "".
["GET", time, key]: return the current value, or "null" when the key is absent or expired.
["DELETE", time, key]: remove the current value and return "true". Return "false" when the key is absent or expired.

Expiration and ordering

A time-limited value written at time t with lifetime d is available during [t, t + d). It is already expired at t + d.
A value written by ordinary SET never expires. It remains until another write replaces it or a successful deletion removes it.
Expiration is checked before processing an operation at that time. Overwritten and deleted values never reappear.
Operation times are nondecreasing. Operations with equal times are processed in their input order.
All times and lifetimes are decimal strings inside the rows. Return the results in the same order as the operations.

Function

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

Examples

Example 1

operations = [["SET_TTL","1","session","open","4"],["GET","4","session"],["GET","5","session"],["SET","5","mode","quiet"],["GET","100","mode"]]return = ["","open","null","","quiet"]

session is valid from time 1 through times strictly less than 5. It is absent at time 5. The ordinary SET for mode has no expiration.

Example 2

operations = [["SET_TTL","10","item","old","2"],["SET","11","item","new"],["GET","50","item"],["DELETE","50","item"],["GET","50","item"]]return = ["","","new","true","null"]

The ordinary SET replaces both the old value and its deadline. The replacement survives time 12. At time 50, the operations run in their listed order.

Constraints

1 <= operations.length <= 100000.
Every row is one of the four valid operation forms above.
Times are nondecreasing integers in [0, 10^15].
Lifetimes are integers in [1, 10^15].
Keys and values contain 1 to 50 ASCII letters, digits, or underscores.