/* package whatever; // don't place package name! */
 
import java.util.*;
import java.lang.*;
import java.io.*;
 
/* Name of the class has to be "Main" only if the class is public. */
class Main
{
	public static void main (String[] args) throws java.lang.Exception
	{
		int arr[] = {1,2,3,4,5};
            int k = 2;
            int count =0;
            HashMap<Integer,Integer> map = new HashMap<>();
            for(int j : arr){
                int temp = j-k;
 
                if(map.containsKey(temp)){
                    count += map.get(temp);
                }
                map.put(j,map.getOrDefault(j,0)+1);
            }
            System.out.println("count => "+count);
	}
}

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