Argus , Beijing 2004 ,LA 3135

题目描述

A data stream is a real-time, continuous, ordered sequence of items. Some examples include sensor data, Internet traffic, financial tickers, on-line auctions, and transaction logs such as Web usage logs and telephone call records. Likewise, queries over streams run continuously over a period of time and incrementally return new results as new data arrives. For example, a temperature detection system of a factory warehouse may run queries like the following. 

 Query-1: "Every five minutes, retrieve the maximum temperature over the past five minutes." 
Query-2: "Return the average temperature measured on each floor over the past 10 minutes."

We have developed a Data Stream Management System called Argus, which processes the queries over the data streams. Users can register queries to the Argus. Argus will keep the queries running over the changing data and return the results to the corresponding user with the desired frequency. 

For the Argus, we use the following instruction to register a query: 

 Register Q_num Period

Q_num (0 < Q_num <= 3000) is query ID-number, and Period (0 < Period <= 3000) is the interval between two consecutive returns of the result. After Period seconds of register, the result will be returned for the first time, and after that, the result will be returned every Period seconds. 

Here we have several different queries registered in Argus at once. It is confirmed that all the queries have different Q_num. Your task is to tell the first K queries to return the results. If two or more queries are to return the results at the same time, they will return the results one by one in the ascending order of Q_num. 

输入

The first part of the input are the register instructions to Argus, one instruction per line. You can assume the number of the instructions will not exceed 1000, and all these instructions are executed at the same time. This part is ended with a line of "#". 

The second part is your task. This part contains only one line, which is one positive integer K (<= 10000). 

输出

You should output the Q_num of the first K queries to return the results, one number per line.

样例输入

Register 2004 200Register 2005 300#5

样例输出

20042005200420042005

题目解说：

你的任务是编写一个称为Argus的系统。该系统支持一个Register命令

                     Register num period

该命令注册了一个触发器，它每Period秒钟就会产生一次编号为num的事件。你的任务是模拟出前k个事件。如果多个事件同时发生，先处理num小的时间。

【输入格式】

输入仅包含一组数据。前若干行是Register命令，以“#”结尾；最后一行是整数k。对于每条命令，1<=num,period<=3 000。k<=10 000。命令条数n不超过1 000。

【输出格式】

输出k行，即前k个事件的num。

【分析】

用优先队列来维护每个触发器的“下一个事件”，然后每次从中取出最早发生的一个事件，重复k次即可。任何时刻优先队列中都是n个元素，因此总时间复杂度为O(klogn)。

CODE：

#include <iostream>
#include <queue>
using namespace std;

//优先队列中的元素 
struct ID{
	int num, period, time;
	//重要！优先级比较函数。优先级高的先出队 
	bool operator < (const ID& x) const{ //这里的const必不可少，请读者注意 
		return time > x.time || (time == x.time && num > x.num);
	}
};

int main(){
	priority_queue<ID> p;
	char s[20];
	
	while(cin>>s && s[0] != '#'){
		ID id;
		cin>>id.num>>id.period;
		id.time = id.period;	//初始化“下一次事件的时间”为它的周期 
		p.push(id); 
	}
	
	int k;
	cin>>k;
	while(k--){
		ID id2 = p.top();	//取下一个周期 
		p.pop();
		cout<<id2.num<<endl;
		id2.time += id2.period;	//更新该触发器的“下一个事件”的时间 
		p.push(id2); 			//重新插入优先队列 
	}
	return 0;
}