HDU 4006 The kth great number 【优先队列+STL】

最新推荐文章于 2021-08-04 23:26:15 发布

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最新推荐文章于 2021-08-04 23:26:15 发布

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分类专栏：栈、队列和STL

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本文介绍了HDU4006题目的解题思路，通过维护一个优先队列或使用multiset，实现了在一系列输入中快速找到第k大的数。提供了两种AC代码示例，一种使用优先队列，另一种使用STL的multiset。

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传送门：HDU 4006

The kth great number Time Limit: 2000/1000 MS (Java/Others) Memory Limit: 65768/65768 K (Java/Others) Total Submission(s): 16237 Accepted Submission(s): 6114

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).

题意：
题意很简单，就是让你每次输出第k大的数

题解：
有两种方法：

方法一：
维护一个由小到大排序的优先队列，优先队列只存k个数，保证队首永远是第k大的数，一旦遇到比队首大的，就把队首弹出，压入大的数。

方法二：
用STL里的multiset来模拟优先队列。
(multiset 将数存入后由小到大排序)

AC代码：

优先队列实现：

#include<iostream>
#include<cstring>
#include<algorithm>
#include<cstdio>
#include<queue>
#define ll long long
#define inf 0x3f3f3f3f
using namespace std;
int n,k;
char c[10];
priority_queue<int,vector<int>,greater<int> >q;
int num;
int main()
{
  while(scanf("%d%d",&n,&k)!=EOF)
  {
    while(!q.empty()) q.pop();
    for(int i=0;i<n;i++)
    {
      scanf("%s",c);
      if(c[0]=='I')
      {
        scanf("%d",&num);
        if(q.size()<k)
        {
          q.push(num);
        }
        else if(q.top()<num)
        {
          q.pop();
          q.push(num);
        }
      }
      else
        printf("%d\n",q.top());
    }
  }
  return 0;
}

STL实现：

#include<iostream>
#include<cstdio>
#include<cstring>
#include<cmath>
#include<algorithm>
#include<set>
#define ll long long
#define inf 0x3f3f3f3f
using namespace std;
int n,k;
int num;
char c[10];

int main()
{
  while(scanf("%d%d",&n,&k)!=EOF)
  {
    multiset<int> a;
    for(int i=0;i<n;i++)
    {
      scanf("%s",c);
      if(c[0]=='I')
      {
        scanf("%d",&num);
        a.insert(num);
        if(a.size()>k)
        {
          a.erase(a.begin());
        }
      }
      else
        printf("%d\n",*a.begin());
    }
  }
  return 0;
}