Quick sort template

Title Description

 

#include <iostream>

using namespace std;

const int N = 100010;

int n, q[N];

void quick_sort(int l, int r)
{
	if(l >= r) return ;
	
	int x = q[l + r >> 1], i = l - 1, j = r + 1;		// the reason being that do i ++, So stagger at the beginning 1 position , Then go in, just from l and r Start  
	
	while(i < j)	
	{
		do i ++ ; while(q[i] < x);			// Because after the exchange ,i Go ahead ,j Go back , So simply do i ++  To write  
		do j -- ; while(q[j] > x);
		
		if(i < j) swap(q[i], q[j]);
	}
	// Because the condition of out circulation is i > j, So either i == j, So divide the region l~j,j+1~r 
	quick_sort(l, j);
	quick_sort(j + 1, r);
}

int main()
{
	scanf("%d", &n);
	for(int i = 0; i < n; i ++ ) scanf("%d", &q[i]);
	
	quick_sort(0, n - 1);
	
	for(int i = 0; i < n; i ++ ) printf("%d ", q[i]);
}

Extended topics :  The first k Number

Title Description ：

  Code ：

#include <iostream>

using namespace std;

const int N = 100010;

int n, q[N], k;
int ans;

void quick_sort(int l, int r, int k)
{
	if(l >= r)
	{
		ans = q[l];
		return ;
	}
	
	int x = q[l + r >> 1], i = l - 1, j = r + 1;		// the reason being that do i ++, So stagger at the beginning 1 position , Then go in, just from l and r Start  
	
	while(i < j)	
	{
		do i ++ ; while(q[i] < x);			// Because after the exchange ,i Go ahead ,j Go back , So simply do i ++  To write  
		do j -- ; while(q[j] > x);
		
		if(i < j) swap(q[i], q[j]);
	}
	// Because the condition of out circulation is i < j, So either i == j, So divide the region l~j,j+1~r 
	if(j - l + 1 >= k)
	quick_sort(l, j, k);
	else
	quick_sort(j + 1, r, k - (j - l + 1));
}

int main()
{
	scanf("%d%d", &n, &k);
	for(int i = 0; i < n; i ++ ) scanf("%d", &q[i]);
	
	quick_sort(0, n - 1, k);
	
	printf("%d", ans);
	return 0;
}