bool binary_search(int* arr, int target, int l, int r){
    while(l <= r){
        int mid = l + (r-l)/2;
        if (arr[mid] == target){
            return true;
        }
        else if (arr[mid] > target){
            r = mid-1;
        }
        else{
            l = mid+1;
        }
    }
    return false;
}

void swap(int* a, int* b){
    int temp = *a;
    *a = *b;
    *b = temp;
}

int partition(int* arr, int l, int r){
    int pivot = arr[r];
    int start_idx = l;
    int bigger_idx = l;
    for (int i = start_idx; i<r; i++){
        if (arr[i] < pivot){
            swap(&arr[i], &arr[bigger_idx]);
            bigger_idx ++;
        }
    }
    swap(&arr[r], &arr[bigger_idx]);
    return bigger_idx;
}

int* my_q_sort(int* arr, int l, int r){
    if (l < r){
        int idx = partition(arr, l, r);
        my_q_sort(arr, l, idx-1);
        my_q_sort(arr, idx+1, r);
    }
    return arr;
}

int pairs(int k, int arr_count, int* arr) {
    int res_count = 0;
    arr = my_q_sort(arr, 0, arr_count-1);
    for (int i = 0; i<arr_count-1; i++){
        bool find_pair = binary_search(arr, arr[i]+k, 0, arr_count-1);
        if (find_pair == true){
            res_count ++;
        } 
    }
    return res_count;
}