STL优先队列-HDU-1509Windows Message Queue

今天药忘吃喽~ 2022-05-26 00:34 213阅读 0赞

# STL优先队列 #

在优先队列中，元素被赋予优先级，当访问元素时，具有最高级优先级的元素先被访问。即优先队列具有最高级先出的行为特征。

优先队列在头文件\#include <queue>中；

其声明格式为：priority\_queue <int> ans;//声明一个名为ans的整形的优先队列

基本操作有：

empty( )  //判断一个队列是否为空

pop( )  //删除队顶元素

push( )  //加入一个元素

size( )  //返回优先队列中拥有的元素个数

top( )  //返回优先队列的队顶元素

优先队列的时间复杂度为O（logn），n为队列中元素的个数，其存取都需要时间。

在默认的优先队列中，优先级最高的先出队。默认的int类型的优先队列中先出队的为队列中较大的数。

#include <iostream>
    #include <vector>
    #include <queue>
    using namespace std;
    int tmp[100];
    struct cmp1
    {
         bool operator ()(int x, int y)
        {
            return x > y;//小的优先级高
        }
    };
    struct cmp2
    {
        bool operator ()(const int x, const int y)
        {
            return tmp[x] > tmp[y]; 
            //tmp[]小的优先级高，由于可以在队外改变队内的值，
            //所以使用此方法达不到真正的优先，建议用结构体类型。
        }
    };
    struct node
    {
        int x, y;
        friend bool operator < (node a, node b)
        {
            return a.x > b.x;//结构体中，x小的优先级高
        }
    };
    
    priority_queue<int>q1;
    priority_queue<int, vector<int>, cmp1>q2;

# Windows Message Queue #

#### Problem Description ####

Message queue is the basic fundamental of windows system. For each process, the system maintains a message queue. If something happens to this process, such as mouse click, text change, the system will add a message to the queue. Meanwhile, the process will do a loop for getting message from the queue according to the priority value if it is not empty. Note that the less priority value means the higher priority. In this problem, you are asked to simulate the message queue for putting messages to and getting message from the message queue.

#### Input ####

There's only one test case in the input. Each line is a command, "GET" or "PUT", which means getting message or putting message. If the command is "PUT", there're one string means the message name and two integer means the parameter and priority followed by. There will be at most 60000 command. Note that one message can appear twice or more and if two messages have the same priority, the one comes first will be processed first.(i.e., FIFO for the same priority.) Process to the end-of-file.

#### Output ####

For each "GET" command, output the command getting from the message queue with the name and parameter in one line. If there's no message in the queue, output "EMPTY QUEUE!". There's no output for "PUT" command.

#### Sample Input ####

GET

PUT msg1 10 5

PUT msg2 10 4

GET

#### Sample Output ####

EMPTY QUEUE!

msg2 10

msg1 10

EMPTY QUEUE!

题意：模拟消息队列，get获得数据，put 放入数据，第一个为字符串代表数据的名称，第二个值为数据值，第三个数为优先级，数越小，优先级越高。

#include<bits/stdc++.h>
    using namespace std;
    struct que
    {
        char a[100];
        int value;
        int p;///优先级
        int f;///先后
        bool friend operator < (que a,que b){
    		if (a.p == b.p)
    		return a.f > b.f;
    		return a.p > b.p;     //越大优先级越小
    	}
    }qq;
    int main()
    {
    	char get[4];
    	priority_queue<que> q;
    	int k = 1;
    	while (~scanf("%s",get)){
    		if (get[0] == 'G'){
    			if (q.empty()){
    				printf("EMPTY QUEUE!\n");
    			}
    			else {
    				qq = q.top();
    				printf("%s %d\n",qq.a,qq.value);
    				q.pop();
    			}
    		}
    		else {
    			scanf("%s %d %d",qq.a,&qq.value,&qq.p);
    			qq.f = k;
    			k++;
    			q.push(qq);
    		}
        }
    	return 0;
    }