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Problem · Hash Table

Authentication System

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Problem statement

Implement a session-based authentication system that manages user sessions using unique token IDs and a configurable time-to-live (time_to_live, or TTL) measured in seconds.

When a token is generated, its expiration time is current_time + time_to_live. A token may be renewed only while it is still unexpired; a successful renewal resets its expiration time to current_time + time_to_live.

Process every string in queries in the given order. The system must support these three operations:

  1. generate <token_id> <current_time>: At current_time, create a new token with the specified ID. Its expiration time is current_time + time_to_live.
  2. renew <token_id> <current_time>: At current_time, extend an existing unexpired token's expiration time to current_time + time_to_live. Ignore the request if the token does not exist or has already expired.
  3. count <current_time>: Return the number of unexpired tokens at current_time.

Important: Token expiration is evaluated before processing any action at the same timestamp. If a token's expiration time is exactly equal to current_time, the token is expired and cannot be renewed or counted.

Function

getUnexpiredTokens(time_to_live: int, queries: String[]) → int[]

Examples

Example 1

time_to_live = 5queries = ["generate aaa 1","renew aaa 2","count 6","generate bbb 7","renew aaa 8","renew bbb 10","count 15"]return = [1,0]

At time 6, token aaa is the only unexpired token, so the first count is 1. At time 15, all tokens have expired, so the second count is 0.

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public int[] getUnexpiredTokens(int time_to_live, String[] queries) {
  // write your code here
}
time_to_live5
queries["generate aaa 1","renew aaa 2","count 6","generate bbb 7","renew aaa 8","renew bbb 10","count 15"]
expected[1,0]
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