Argus(ZOJ Problem Set - 2212)(优先队列)

Argus 分享至QQ空间 去爱问答提问或回答

时间限制(普通/Java):1000MS/3000MS     运行内存限制:65536KByte
总提交: 3            测试通过: 2

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 200
Register 2005 300
#
5

样例输出

2004
2005
2004
2004
2005

题目来源

Beijing 2004

题目上传者

crq


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

struct Instrut
{
	int id;
	double ReturnTime; 
	double period;
	Instrut(int i, double p):id(i), ReturnTime(p), period(p){}

};

bool operator < (const Instrut& x, const Instrut& y)
{
    if(x.ReturnTime != y.ReturnTime)
        return x.ReturnTime > y.ReturnTime;
    return x.id > y.id;
}

int main()
{
	string str;
	int k, id, period;
	priority_queue<Instrut> que;
	for(int i = 0; cin >> str; ++i)
	{
		if(str == "#") break;
		else
			cin >> id >> period;
        Instrut tmp(id, period);
        que.push(tmp);
	}
    cin >> k;
    while(k--)
    {
        Instrut tmp = que.top();
        que.pop();
        cout << tmp.id << endl;
        tmp.ReturnTime += tmp.period;
        que.push(tmp);
    }
	return 0;
}


Antique Comedians of Malidinesia would like to play a new discovered comedy of Aristofanes. Putting it on a stage should be a big surprise for the audience so all the preparations must be kept absolutely secret. The ACM director suspects one of his competitors of reading his correspondece. To prevent other companies from revealing his secret, he decided to use a substitution cipher in all the letters mentioning the new play. Substitution cipher is defined by a substitution table assigning each character of the substitution alphabet another character of the same alphabet. The assignment is a bijection (to each character exactly one character is assigned -- not neccessary different). The director is afraid of disclosing the substitution table and therefore he changes it frequently. After each change he chooses a few words from a dictionary by random, encrypts them and sends them together with an encrypted message. The plain (i.e. non-encrypted) words are sent by a secure channel, not by mail. The recipient of the message can then compare plain and encrypted words and create a new substitution table. Unfortunately, one of the ACM cipher specialists have found that this system is sometimes insecure. Some messages can be decrypted by the rival company even without knowing the plain words. The reason is that when the director chooses the words from the dictionary and encrypts them, he never changes their order (the words in the dictionary are lexicographically sorted). String a1a2 ... ap is lexicografically smaller than b1b2 ... bq if there exists an integer i, i <= p, i <= q, such that aj=bj for each j, 1 <= j < i and ai < bi. The director is interested in which of his messages could be read by the rival company. You are to write a program to determine that. Input Output Sample Input 2 5 6 cebdbac cac ecd dca aba bac cedab 4 4 cca cad aac bca bdac Sample Output abcde Message cannot be decrypted.
#### 含义 `nonce` 是一个一次性使用的随机数,在 `nonce="argus-csp-token-argus"` 中,`nonce` 是一个属性,而 `"argus-csp-token-argus"` 是为该属性赋予的具体值。这个值通常是服务器端生成的唯一且随机的字符串,用于特定的安全验证场景。 #### 用途 在内容安全策略(Content Security Policy,CSP)中,`nonce` 扮演着重要角色。CSP 是一种额外的安全层,用于检测并缓解某些类型的攻击,包括跨站脚本攻击(XSS)和数据注入攻击等。服务器可以通过设置 CSP 头,指定哪些资源(如脚本、样式表等)可以被页面加载。使用 `nonce` 可以精确控制哪些资源能够被执行。 例如,服务器可以在响应头中设置如下的 CSP 规则: ``` Content-Security-Policy: script-src 'nonce-argus-csp-token-argus'; ``` 这意味着只有带有 `nonce="argus-csp-token-argus"` 属性的 `<script>` 标签内的脚本才会被浏览器执行。示例代码如下: ```html <!DOCTYPE html> <html> <head> <meta http-equiv="Content-Security-Policy" content="script-src 'nonce-argus-csp-token-argus'"> </head> <body> <!-- 这个脚本会被执行 --> <script nonce="argus-csp-token-argus"> console.log('This script is allowed.'); </script> <!-- 这个脚本不会被执行 --> <script> console.log('This script is blocked.'); </script> </body> </html> ``` #### 相关 IT 知识 - **安全性**:使用 `nonce` 可以有效防止 XSS 攻击,因为攻击者无法预测服务器生成的随机 `nonce` 值,所以他们注入的脚本无法通过 CSP 的验证。 - **生成与管理**:`nonce` 值必须由服务器端生成,并且每个页面加载时都应该是唯一的。服务器需要在生成响应时将 `nonce` 值嵌入到 CSP 头和相应的 HTML 标签中。 - **兼容性**:大多数现代浏览器都支持 CSP 和 `nonce` 属性,但在使用时仍需考虑旧版本浏览器的兼容性问题。
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