import java.util.HashMap;
 
public class Main {
    public static int countPairsWithDifferenceK(int[] b, int k) {
        HashMap<Integer, Integer> freq = new HashMap<>();
        int count = 0;
 
        for (int j = 0; j < b.length; ++j) {
            if (freq.containsKey(b[j] - k)) {
                count += freq.get(b[j] - k);
            }
            if (k != 0 && freq.containsKey(b[j] + k)) { // to avoid double counting when k = 0
                count += freq.get(b[j] + k);
            }
 
            freq.put(b[j], freq.getOrDefault(b[j], 0) + 1);
        }
 
        return count;
    }
 
    public static void main(String[] args) {
        int[] b = {1, 5, 3, 4, 2};
        int k = 2;
        System.out.println(countPairsWithDifferenceK(b, k)); // Output should be the number of pairs with difference k
    }
}

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