/* package whatever; // don't place package name! */
 
import java.util.*;
import java.lang.*;
import java.io.*;
 
class Ideone {
	public static void main (String[] args) throws java.lang.Exception {
		int[] arr = {1, 5, 2, 2, 3};
		int k = 1;
		Map<Integer, Integer> map = new HashMap<>();
		int count = 0;
 
		for (int i = 0; i < arr.length; i++) {
			int need = arr[i] - k;
			if (map.containsKey(need)) {
				count += map.get(need);
			}
			map.put(arr[i], map.getOrDefault(arr[i], 0) + 1);
		}
 
		System.out.println("Total pairs: " + count);
	}
}
 

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