求第K大数[STL:nth_element]

输入n,k,求第k大

5 2
5 4 1 3 1

结果：4

#include<cstdio>
#include<cmath>
#include<cstring>
#include<set>
#include<stack>
#include<queue>
#include<vector>
#include<iostream>
#include<algorithm>
using namespace std;
#define ll long long
#define INF 0x7FFFFFFF
#define INT_MIN -(1<<31)
#define eps 10^(-6)
#define Q_CIN ios::sync_with_stdio(false)
#define REP( i,n ) for ( int i = 0 ; i < n ; ++ i )
#define REV( i,n ) for ( int i = n - 1 ; i >= 0 ; -- i )
#define FOR( i,a,b ) for ( int i = a ; i <= b ; ++ i )
#define FOV( i,b ) for ( int i = a ; i >= b ; -- i )
#define CLR( a,x ) memset ( a,x,sizeof (a) )
#define RE freopen("in.txt","r",stdin)
#define WE freopen("out.txt","w",stdout)
#define NMAX 10002
#define min(a,b) ((a)>(b)?(b):(a))
int read()
{
    int x=0,f=1;char ch=getchar();
    while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();}
    while(ch>='0'&&ch<='9'){x=x*10+ch-'0';ch=getchar();}
    return x*f;
}
int arr[5000100];

int main()
{
    int n,k;
    RE;
    while(~scanf("%d%d",&n,&k))
    {
        REP(i,n)
            arr[i] = read();
        nth_element(arr,arr+(n-k),arr+n);
        printf("%dn",arr[n-k]);
    }
    return 0;
}