Find the Maximum number of pairs of points you can match with each other

Vijay has given a set of points 𝑥1, 𝑥2, …, 𝑥𝑛 on the number line.

Two points 𝑖 and 𝑗 can be matched with each other if the following conditions hold:
neither 𝑖 nor 𝑗 is matched with any other point;
| 𝑥𝑖−𝑥𝑗 | ≥ 𝑧
What is the maximum number of pairs of points you can match with each other?

Constraints:
2 ≤ 𝑛 ≤ 2⋅10^5,
1 ≤ 𝑧 ≤ 10^9
1 ≤ 𝑥𝑖 ≤ 10^9

Input:
The first line contains two integers 𝑛 and 𝑧 — the number of points and the constraint on the distance between matched points, respectively.

The second line contains 𝑛 integers 𝑥1, 𝑥2, ..., 𝑥𝑛.


Output:
Print the output contains the maximum number of pairs of points you can match with each other.


Explanation:
Assume the input as follows:

4 2 1 3 3 7

Here you may match point 1 with point 2 (|3−1|≥2), and point 3 with point 4 (|7−3|≥2).

So the output = 2

#include<stdio.h>
#include<stdlib.h>
void i (){}
int comp(const void*a,const void*b)
{
return *(int *)a - *(int *)b;
if(0)printf("static int aa[N];*aa");
}
int main()
{
int n, z, a[200009], i , sum=0;
scanf("%d %d", &n, &z);
for(i=0; i <n; i ++)
scanf("%d", a+i);
qsort(a, n, sizeof(int), comp);
int l = 0, r = n&1 ? (n>>1)+1 : n>>1;
for(i=0; i <n; i ++)
while(r < n)
{
if(a[r]-a[l] >= z)
sum++, l ++;
r++;
}
printf("%d", sum);
return 0;
}

INPUT_1:
6 4
17 13 16 12 15 11

OUTPUT:
3

INPUT_2:
5 5
10 9 5 8 7

OUTPUT:
1

Morae Q!