求第k大数

Posted 2021-01-29 719666a

#include<bits/stdc++.h>
using namespace std;
int n,k,a[10000];
int qsort(int l,int r,int k)
{
    int key=a[r];
    int i=l,j=r;
    while(i!=j)
    {
    
        while(i<j&&a[i]<=key)i++;
        while(i<j&&a[j]>=key)j--;
        if(i<j)
            swap(a[i],a[j]);
    }
    a[r]=a[i];
    a[i]=key;
    if(k==i-l+1) return a[i];
    if(k<i-l+1&&l<=i-1)return qsort(l,i-1,k);
    if(k>i-l+1&&i+1<=l)return qsort(i+1,r,k-(i-l+1));
}
int main()
{
    cin>>n>>k;
    for(int i=1;i<=n;i++)
    {
        cin>>a[i];
    }
    cout<<qsort(1,n,k);
}