public static int pairs(int k, List<Integer> arr) {
    // Create a HashSet for quick lookups
    HashSet<Integer> set = new HashSet<>(arr);
    int numOfpairs = 0;

    // Loop through each element in the set
    for (int num : set) {
        // Check if the pair (num + k) exists in the set
        if (set.contains(num - k)) {
            numOfpairs++;
        }
    }
    
    return numOfpairs;
}