CSU 1867 中南大学网络赛F题 John and Health rate

题目：

Description

The cold and flu season is here.John is worried about his cow. In order to monitor the situation of his cow,he do some inspecting everyday,and record the “health rate” for each cow.The
“health rate” is a integer which can show the cow’s health condition.The higher a cow’s health rate is ,the healthier the cow is.What’s more,the doctor told John that the k-th small health rate is dangerous.Because the doctor thought there are at most k healthy
cows. So John has to find out which number is the k-th small.Can you help him?

Input

Input contains multiple test cases.

The first line contains two integers n,k (1 ≤ n ≤ 1000000,1<=k<=n) — the number of cows and dangerous number. The second line contains n integers,and the i-th integer ai(-10000<=ai<=10000) is the i-th cow’s health rate

Output

Output a single line with the k-th small health rate.

Sample Input

2 1
3 2
5 2
-1 0 -2 5 3

Sample Output

2
-1

就是输入n,k，然后输入n个数，要求输出从小到大第k个数。

线性时间选择的算法是比较复杂的，这里不需要，因为给出了每个数的范围，所以只需要20001个桶即可。

代码：

#include<iostream>
using namespace std;

int num[20001];

int main()
{
int n, k, h, key;
while (cin >> n >> k)
{
for (int i = 0; i <= 20000; i++)num[i] = 0;
for (int i = 0; i < n; i++)
{
scanf("%d", &h);
num[h + 10000]++;
}
key = 0;
while (k>num[key])k -= num[key++];
cout << key - 10000 << endl;
}
return 0;
}