DesignAuthenticationManager.cpp

// Source : https://leetcode.com/problems/design-authentication-manager/
// Author : Hao Chen
// Date   : 2021-03-22

/***************************************************************************************************** 
 *
 * 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 <= 10^8
 * 	1 <= currentTime <= 10^8
 * 	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.
 ******************************************************************************************************/

class AuthenticationManager {
private: 
    int ttl;
    set<pair<int, string>> time_set;
    unordered_map<string, int> token_map;
public:
    AuthenticationManager(int timeToLive):ttl(timeToLive) { }
    
    void generate(string tokenId, int currentTime) {
        token_map[tokenId] = currentTime;
        time_set.insert({currentTime, tokenId});
    }
    
    void renew(string tokenId, int currentTime) {
        //if the token is not found, or the token is expired
        if (token_map.find(tokenId) == token_map.end() ||
            token_map[tokenId] + ttl <= currentTime ) {
            return;
        }
        time_set.erase({token_map[tokenId], tokenId});
        time_set.insert({currentTime, tokenId});
        token_map[tokenId] = currentTime;
    }
    
    int countUnexpiredTokens(int currentTime) {
        return clean(currentTime - ttl);
    }
    
    int clean(int expired) {

        auto it = time_set.begin();
        while(!time_set.empty() && it->first <= expired) {
            token_map.erase(it->second);
            time_set.erase(it);
            it = time_set.begin();
        }
        return time_set.size();
    }
};

/**
 * Your AuthenticationManager object will be instantiated and called as such:
 * AuthenticationManager* obj = new AuthenticationManager(timeToLive);
 * obj->generate(tokenId,currentTime);
 * obj->renew(tokenId,currentTime);
 * int param_3 = obj->countUnexpiredTokens(currentTime);
 */