int comp(const void *a, const void *b) {
    return (*(int*)b - *(int*)a);
}

int pairs(int k, int arr_count, int* arr) {
    int p1 = 0;
    int p2 = 1;
    int count = 0;
    qsort(arr, arr_count, sizeof(int), comp);
    while(p2 < arr_count) {
        long long d = arr[p1] - arr[p2];
        ++p2;
        if(d == k) ++count;
        else if (d > k || p2 >= arr_count) {
            ++p1;
            p2 = p1 + 1;
        }
    }
    return count;
}

sub pairs {
    my $k = shift;
    my $arr = shift;
    my $res = 0;

    my %h = map {$_ => 1} @$arr;
    foreach my $key (keys %h) {
        $res++ if (exists($h{$k + $key}));
    }

    return $res;
}

int pairs(int k, vector<int> arr) {
    int ret = 0;
    set<int> lookup(arr.begin(), arr.end());
    for(auto itr : arr) if(lookup.find(itr + k) != lookup.end()) ret++;
    return ret;
}

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;
}

def pairs(k, arr):
    arr = set(arr)
    ans = 0
    for i in arr:
        if i + k in arr:
            ans += 1
    return ans