Qsort求静态的第K大

Who is in the middle

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#include<iostream>
#include<cmath>
#include<cstdlib>
#include<utility>
using namespace std;
const int maxN=2e6+10;
int n,a[maxN],k;
 
int find(int l,int r,int k)
{
    if(l==r)
        return a[l];
    int t=a[(l+r)/2];
    int i=l,j=r;
    while(i<=j)
    {
        while(a[i]<t)i++;
        while(a[j]>t)j--;
        if(i<=j){
            swap(a[i],a[j]);
            i++;
            j--;
        }
    }
    if(k<=j-l+1)
        return find(l,j,k);
    else if(k>i-l)
        return find(i,r,k-(i-l));
    else
        return t;
}
 
int main()
{
    cin>>n;
    k=(1+n)/2;
    for(int i=1;i<=n;++i)
        cin>>a[i];
 
    cout<<find(1,n,k)<<endl;
    return 0;
}

  

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