o(n) algorithm for finding the number of pairs that have a difference of k

Pairs.cs

using System;
using System.Collections.Generic;

class Solution 
{
    //Get N and K
    // Read N and split.
    // scan N array
    //create a bucket
    //count =0
        // if bucket contains n-2 then c++
        //if bucket contains n+2 then c++
        // add number to bucket.
        // 5 2
        // 1 5 3 4 2
    static void Main()
    {
        string[] nk = Console.ReadLine().Split(' ');
        int n = int.Parse(nk[0]);
        int k = int.Parse(nk[1]);
        string[] a = Console.ReadLine().Split(' ');
        HashSet<int> s = new HashSet<int>();
        int count=0;
        for (int i = 0; i < n; i++)
        {
            int e = int.Parse(a[i]);
            if (s.Contains(e - k))
                count++;
            if (s.Contains(e + k))
                count++;
            s.Add(e);
        }
        Console.WriteLine(count);
    }
}