[Leetcode] 359. Logger Rate Limiter 解题报告

题目：

Design a logger system that receive stream of messages along with its timestamps, each message should be printed if and only if it is not printed in the last 10 seconds.

Given a message and a timestamp (in seconds granularity), return true if the message should be printed in the given timestamp, otherwise returns false.

It is possible that several messages arrive roughly at the same time.

Example:

Logger logger = new Logger();

// logging string "foo" at timestamp 1
logger.shouldPrintMessage(1, "foo"); returns true; 

// logging string "bar" at timestamp 2
logger.shouldPrintMessage(2,"bar"); returns true;

// logging string "foo" at timestamp 3
logger.shouldPrintMessage(3,"foo"); returns false;

// logging string "bar" at timestamp 8
logger.shouldPrintMessage(8,"bar"); returns false;

// logging string "foo" at timestamp 10
logger.shouldPrintMessage(10,"foo"); returns false;

// logging string "foo" at timestamp 11
logger.shouldPrintMessage(11,"foo"); returns true;

思路：

一道相对比较简单的design类题目。我们定义的数据结构是一个哈希表，里面保存了日志的内容和上一次打印时间。然后到收到一个新的消息时，我们查看在哈希表中是否已经存在该日志，如果不存在，则记录打印时间，并打印；如果已经存在，则看起上一次打印的时间戳，如果在十秒之内，则不打印，否则就需要更新时间戳，并打印。

代码：

class Logger {
public:
    /** Initialize your data structure here. */
    Logger() {
        
    }
    
    /** Returns true if the message should be printed in the given timestamp, otherwise returns false.
        If this method returns false, the message will not be printed.
        The timestamp is in seconds granularity. */
    bool shouldPrintMessage(int timestamp, string message) {
        if(hash.count(message) == 0) {
            hash[message] = timestamp;
            return true;
        }
        else {
            int time_stamp = hash[message];
            if(timestamp - time_stamp >= 10) {
                hash[message] = timestamp;
                return true;
            }
            else {
                return false;
            }
        }
    }
private:
    unordered_map<string, int> hash;	// value stores the time stamp that this log was printed last time
};

/**
 * Your Logger object will be instantiated and called as such:
 * Logger obj = new Logger();
 * bool param_1 = obj.shouldPrintMessage(timestamp,message);
 */