最后两个超时

#include <iostream>
#include<vector>
#include<algorithm>
using namespace std;

vector<int> a(50000005);

void quick(vector<int> &a,int low, int high, int k)
{
    if(low <= high)
    {
        int i = low, j = high;
        int x = a[i];
        while(i < j)
        {
            while(i < j && a[j] >= x) j--;
            a[i] = a[j];
            while(i < j && a[i] <= x) i++;
            a[j] = a[i];
        }
        a[i] = x;
        //cout << i << " " << x << endl;
        if(i == k)
        {
            cout << x;
            return;
        }
        else if(k < i)
        {
            quick(a,low, i-1,k);
            return;
        }
        else
        {
            quick(a,i+1, high,k);
            return;
        }

    }
}

int main()
{
    int n,k;
    cin >> n >> k;  
    for(int i = 0; i < n; i++)
    {
        cin >> a[i];
    }
    quick(a,0,n-1,k);
    return 0;
}