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;
}