vijos1788 第k大

#include<cstdio>
#include<cctype>
#include<algorithm>
using namespace std;
inline int read(){
    char c; while(c=getchar(),!isdigit(c)); int x=c-‘0‘;
    while(c=getchar(),isdigit(c)) x=x*10+c-‘0‘; return x;
}
int a[100001];
int find(int l,int r,int x){
    int i=l,j=r,mid=a[l+r>>1];
    while(i<=j){
        while(i<r && a[i]>mid) i++;
        while(j>l && a[j]<mid) j--;
        if(i<=j) swap(a[i++],a[j--]);
    }
    if(j<x && x<i) return mid;
    if(x<=j) return find(l,j,x);
    if(x>=i) return find(i,r,x);
}
int main(){
    int n=read(),k=read();
    for(int i=1;i<=n;i+=1) a[i]=read();
    printf("%d",find(1,n,k));
    return 0;
}