ACdream 1099——————【快排舍半，输入外挂】

#include<stdio.h>
#include<algorithm>
#include<string.h>
using namespace std;
const int maxn=1e7;
int a[maxn];
int scan(){

    char c;
    int sgn,ret;
    if(c=getchar(),c==EOF)
        return 0;
    while(c!=‘-‘&&(c<‘0‘||c>‘9‘))
        c=getchar();
    sgn=(c==‘-‘)?-1:1;
    ret=(c==‘-‘)?0:(c-‘0‘);
    while(c=getchar(),c>=‘0‘&&c<=‘9‘)
        ret=ret*10+(c-‘0‘);
    ret *=sgn;
    return ret;
}
int mysort(int L,int R,int k){

    if(L==R){       //区间内只有一个值，即为所求第k大值

        return a[L];
    }
    int key=a[L];
    int low=L;
    int high=R;
    while(low<high){
      
        while(low<high&&a[high]<=key)
            high--;
        if(low<high)
            a[low++]=a[high];
        while(low<high&&a[low]>=key)
            low++;
        if(low<high)
            a[high--]=a[low];
    }
    a[low]=key;
    if(low==k)  //该基准值即为第k大的元素
        return a[low];
    else if(low>k)return mysort(L,low-1,k); //舍半逼近
    else return mysort(low+1,R,k);
}
int main(){

    int n , k;
    scanf("%d%d",&n,&k);
    for(int i=0;i<n;i++){

        a[i]=scan();
    }
    int ans=mysort(0,n-1,k-1);
    printf("%d\n",ans);
    return 0;
}