Introduction

In this blog post, we will explore how to solve the LeetCode problem "1797" using AI. LeetCode is a popular platform for preparing for coding interviews, and with the help of AI tools like Chatmagic, we can generate solutions quickly and efficiently - helping you pass the interviews and get the job offer without having to study for months.

Problem Statement

There is an authentication system that works with authentication tokens. For each session, the user will receive a new authentication token that will expire timeToLive seconds after the currentTime. If the token is renewed, the expiry time will be extended to expire timeToLive seconds after the (potentially different) currentTime. Implement the AuthenticationManager class: AuthenticationManager(int timeToLive) constructs the AuthenticationManager and sets the timeToLive. generate(string tokenId, int currentTime) generates a new token with the given tokenId at the given currentTime in seconds. renew(string tokenId, int currentTime) renews the unexpired token with the given tokenId at the given currentTime in seconds. If there are no unexpired tokens with the given tokenId, the request is ignored, and nothing happens. countUnexpiredTokens(int currentTime) returns the number of unexpired tokens at the given currentTime. Note that if a token expires at time t, and another action happens on time t (renew or countUnexpiredTokens), the expiration takes place before the other actions. Example 1: Input ["AuthenticationManager", "renew", "generate", "countUnexpiredTokens", "generate", "renew", "renew", "countUnexpiredTokens"] [[5], ["aaa", 1], ["aaa", 2], [6], ["bbb", 7], ["aaa", 8], ["bbb", 10], [15]] Output [null, null, null, 1, null, null, null, 0] Explanation AuthenticationManager authenticationManager = new AuthenticationManager(5); // Constructs the AuthenticationManager with timeToLive = 5 seconds. authenticationManager.renew("aaa", 1); // No token exists with tokenId "aaa" at time 1, so nothing happens. authenticationManager.generate("aaa", 2); // Generates a new token with tokenId "aaa" at time 2. authenticationManager.countUnexpiredTokens(6); // The token with tokenId "aaa" is the only unexpired one at time 6, so return 1. authenticationManager.generate("bbb", 7); // Generates a new token with tokenId "bbb" at time 7. authenticationManager.renew("aaa", 8); // The token with tokenId "aaa" expired at time 7, and 8 >= 7, so at time 8 the renew request is ignored, and nothing happens. authenticationManager.renew("bbb", 10); // The token with tokenId "bbb" is unexpired at time 10, so the renew request is fulfilled and now the token will expire at time 15. authenticationManager.countUnexpiredTokens(15); // The token with tokenId "bbb" expires at time 15, and the token with tokenId "aaa" expired at time 7, so currently no token is unexpired, so return 0. Constraints: 1 <= timeToLive <= 108 1 <= currentTime <= 108 1 <= tokenId.length <= 5 tokenId consists only of lowercase letters. All calls to generate will contain unique values of tokenId. The values of currentTime across all the function calls will be strictly increasing. At most 2000 calls will be made to all functions combined.

Explanation

• Use a dictionary to store the tokens: This allows for efficient lookup and renewal of tokens by their tokenId. The value stored will be the token's expiration time.
  • Implement the methods according to the problem description: The generate, renew, and countUnexpiredTokens methods will implement the logic for creating tokens, renewing them (if they exist and are not expired), and counting the number of unexpired tokens, respectively.

• Runtime Complexity: O(1) for generate and renew, O(N) for countUnexpiredTokens where N is the number of active tokens. Average O(1) for count if we store only active tokens. Storage Complexity: O(N) where N is the number of active tokens.

Code

    class AuthenticationManager:

    def __init__(self, timeToLive: int):
        self.timeToLive = timeToLive
        self.tokens = {}  # tokenId: expirationTime

    def generate(self, tokenId: str, currentTime: int) -> None:
        self.tokens[tokenId] = currentTime + self.timeToLive

    def renew(self, tokenId: str, currentTime: int) -> None:
        if tokenId in self.tokens and self.tokens[tokenId] > currentTime:
            self.tokens[tokenId] = currentTime + self.timeToLive

    def countUnexpiredTokens(self, currentTime: int) -> int:
        count = 0
        for tokenId, expirationTime in self.tokens.items():
            if expirationTime > currentTime:
                count += 1
        return count