HDU 4006 The kth great number （优先队列）-优快云博客

本文介绍了一个简单而有效的算法，用于找出一组数中第K大的数。通过使用大小为K的优先队列来维护当前最大的K个数，当需要查询第K大数时可以直接输出队首元素。

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The kth great number

Time Limit: 2000/1000 MS (Java/Others) Memory Limit: 65768/65768 K (Java/Others)
Total Submission(s): 9921 Accepted Submission(s): 3950

Problem Description

Xiao Ming and Xiao Bao are playing a simple Numbers game. In a round Xiao Ming can choose to write down a number, or ask Xiao Bao what the kth great number is. Because the number written by Xiao Ming is too much, Xiao Bao is feeling giddy. Now, try to help Xiao Bao.

Input

There are several test cases. For each test case, the first line of input contains two positive integer n, k. Then n lines follow. If Xiao Ming choose to write down a number, there will be an " I" followed by a number that Xiao Ming will write down. If Xiao Ming choose to ask Xiao Bao, there will be a "Q", then you need to output the kth great number.

Output

The output consists of one integer representing the largest number of islands that all lie on one line.

Sample Input

  
   8 3
I 1
I 2
I 3
Q
I 5
Q
I 4
Q

Sample Output

  
   1
2
3


   
    
     Hint
    Xiao  Ming  won't  ask  Xiao  Bao  the  kth  great  number  when  the  number  of  the  written number is smaller than k. (1=<k<=n<=1000000).

Source

The 36th ACM/ICPC Asia Regional Dalian Site —— Online Contest

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找第k的数

思路：维护一个大小为k的优先队列，输出时输出队首元素即可。

#include<cstdio>
#include<cstring>
#include<queue>
#include<algorithm>
using namespace std;
int main()
{
	int i,j,k,l,m,n;
	char s[25];
	while(scanf("%d%d",&n,&k)!=EOF)
	{
		priority_queue<int,vector<int>,greater<int> >q;
		while(n--)
		{
			scanf("%s",s);
			if(strcmp(s,"I")==0)
			{
				scanf("%d",&m);
				if(q.size()<k)
				q.push(m);
				else
				{
					if(m>q.top())
					{
						q.pop();
					    q.push(m);
					}	
				}
			}
			else
			{
				printf("%d\n",q.top());
			}
		}
	}
	return 0;
}