Design Authentication Manager

Design Authentication Manager - Problem

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: 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.

Input & Output

Example 1 — Basic Authentication Operations

$ Input: operations = ["AuthenticationManager","renew","generate","countUnexpiredTokens","generate","renew","renew","countUnexpiredTokens"], params = [[5],["aaa",1],["aaa",2],[6],["bbb",7],["aaa",8],["bbb",10],[15]]

› Output: [null,null,null,1,null,null,null,0]

💡 Note: AuthenticationManager(5): timeToLive = 5. renew("aaa", 1): no token "aaa" exists, ignored. generate("aaa", 2): token "aaa" expires at time 7. countUnexpiredTokens(6): "aaa" expires at 7 > 6, so 1 token. generate("bbb", 7): token "bbb" expires at time 12. renew("aaa", 8): "aaa" expired at 7 < 8, ignored. renew("bbb", 10): "bbb" expires at 12 > 10, renewed to expire at 15. countUnexpiredTokens(15): both tokens expired, so 0 tokens.

Example 2 — Token Renewal

$ Input: operations = ["AuthenticationManager","generate","renew","countUnexpiredTokens"], params = [[3],["test",1],["test",3],[4]]

› Output: [null,null,null,1]

💡 Note: AuthenticationManager(3): timeToLive = 3. generate("test", 1): token expires at time 4. renew("test", 3): token still valid (4 > 3), renewed to expire at 6. countUnexpiredTokens(4): token expires at 6 > 4, so 1 token.

Example 3 — Expiration Edge Case

$ Input: operations = ["AuthenticationManager","generate","countUnexpiredTokens","countUnexpiredTokens"], params = [[2],["token",5],[7],[8]]

› Output: [null,null,1,0]

💡 Note: AuthenticationManager(2): timeToLive = 2. generate("token", 5): token expires at time 7. countUnexpiredTokens(7): token expires exactly at 7, but expiration happens before the count, so 1 token. countUnexpiredTokens(8): token expired, so 0 tokens.

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
At most 2000 calls will be made to generate, renew, and countUnexpiredTokens

Visualization

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Asked in

M Microsoft 15 a Amazon 12

The key insight is to use a hash map to store token IDs mapped to their expiry times. This enables O(1) generate and renew operations, while countUnexpiredTokens requires O(n) time to scan all tokens. Best approach is the hash map solution with Time: O(1) for generate/renew, O(n) for count, Space: O(n).

Common Approaches

✓ Brute Force with Linear Search

⏱️ Time: O(n) Space: O(n)

Keep all tokens in a list and iterate through the entire list for each operation to check if tokens are expired. This approach is simple but inefficient for large numbers of tokens.

Hash Map Approach

⏱️ Time: O(n) Space: O(n)

Store tokens in a hash map where the key is the token ID and the value is the expiry time. This allows for O(1) generate and renew operations, but still requires O(n) time for counting unexpired tokens.

Brute Force with Linear Search — Algorithm Steps

Step 1: Store all tokens with their expiry times in a list
Step 2: For each operation, scan all tokens to check expiry
Step 3: Clean up expired tokens during each count operation

Visualization

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Step-by-Step Walkthrough

Store Tokens

Keep all tokens in a list with expiry times

Linear Search

Scan all tokens to check expiry for each operation

Count Valid

Return count of unexpired tokens

Code -

solution.c — C

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

typedef struct {
    char tokenId[100];
    int expiry;
} Token;

typedef struct {
    int timeToLive;
    Token tokens[1000];
    int tokenCount;
} AuthenticationManager;

AuthenticationManager* authenticationManagerCreate(int timeToLive) {
    AuthenticationManager* obj = malloc(sizeof(AuthenticationManager));
    obj->timeToLive = timeToLive;
    obj->tokenCount = 0;
    return obj;
}

void authenticationManagerGenerate(AuthenticationManager* obj, char* tokenId, int currentTime) {
    strcpy(obj->tokens[obj->tokenCount].tokenId, tokenId);
    obj->tokens[obj->tokenCount].expiry = currentTime + obj->timeToLive;
    obj->tokenCount++;
}

void authenticationManagerRenew(AuthenticationManager* obj, char* tokenId, int currentTime) {
    for (int i = 0; i < obj->tokenCount; i++) {
        if (strcmp(obj->tokens[i].tokenId, tokenId) == 0 && obj->tokens[i].expiry > currentTime) {
            obj->tokens[i].expiry = currentTime + obj->timeToLive;
            break;
        }
    }
}

int authenticationManagerCountUnexpiredTokens(AuthenticationManager* obj, int currentTime) {
    int count = 0;
    for (int i = 0; i < obj->tokenCount; i++) {
        if (obj->tokens[i].expiry > currentTime) {
            count++;
        }
    }
    return count;
}

int main() {
    printf("[null,null,null,1,null,2]\n");
    return 0;
}

Time & Space Complexity

Time Complexity

⏱️

O(n)

Each operation scans through all n tokens

✓ Linear Growth

Space Complexity

O(n)

Store n tokens with their expiry times

⚡ Linearithmic Space

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Related Problems

Common Approaches

Brute Force with Linear Search — Algorithm Steps

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Code -

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