How should I practice Per-Element Hit Counter?

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Is Per-Element Hit Counter associated with Uber?

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Problem · Hash Table

● Medium

UberFULLTIMEONSITE INTERVIEW

Process a chronological batch of hit-counter commands. Each command is one of:

HIT el timestamp records one hit of element el at timestamp.
GET el timestamp returns how many hits of el fall in the half-open window (timestamp - 300, timestamp].
TOTAL timestamp returns how many hits of any element fall in that same window.

Timestamps are positive and non-decreasing. A hit at time t is counted by a query at time q if and only if q - 300 < t <= q.

Return the results of the GET and TOTAL commands in the order they appear.

processHitCounterCommands(commands: String[]) → int[]

commands = ["HIT a 1","HIT b 2","HIT a 2","GET a 2","GET b 2","TOTAL 2"]return = [2,1,3]

At time 2, element a has hits at 1 and 2, element b has one hit, and the three hits together make the total 3.

commands = ["HIT a 1","HIT a 2","HIT b 300","GET a 301","GET b 301","TOTAL 301"]return = [1,1,2]

The query window at time 301 is (1, 301], so the hit of a at time 1 has expired. The remaining hits are a at 2 and b at 300.

1 <= commands.length <= 10000.
Each command is exactly HIT el timestamp, GET el timestamp, or TOTAL timestamp.
Every el is a nonempty string of at most 16 lowercase English letters.
Timestamps are integers in [1, 10^9] and are non-decreasing across the batch.
At least one command is GET or TOTAL.