求助，为什么全部tle，捉虫没捉到

#include<iostream>
#include<random>
#include<cmath>
using namespace std;
int a[5000001], n, k;
int qSearch(int, int, int);
int main(){
    srand(time(0));
    scanf("%d %d", &n, &k);
    for(int i = 0;i < n;i++){
        scanf("%d", &a[i]);
    }
    int q = qSearch(k, 0, n-1);
    printf("%d", q);
}
int qSearch(int k, int l, int r){
    if(l >= r)
        return a[k];
    int t = rand() % (r - l + 1) + l;
    swap(a[r], a[t]);
    int i = l, j = r;
    while(i < j){
        while(a[i] <= a[r] && i < j){
            i++;
        }
        while(a[j] > a[r] && i < j){
            j--;
        }
        swap(a[i], a[j]);
    }
    swap(a[i], a[r]);
    if(k > i)
        return qSearch(k, i+1, r);
    else if(k < i)    return qSearch(k, l, i-1);
    return a[k];
}