Solve the programming task below in a Python markdown code block.
Given an array of integers and a target value, determine the number of pairs of array elements that have a difference equal to the target value.  

Example 

$k=1$ 

$arr=[1,2,3,4]$   

There are three values that differ by $k=1$: $2-1=2$, $3-2=1$, and $4-3=1$.  Return $3$.  

Function Description

Complete the pairs function below.   

pairs has the following parameter(s):

int k: an integer, the target difference
int arr[n]: an array of integers   

Returns   

int: the number of pairs that satisfy the criterion

Input Format

The first line contains two space-separated integers $n$ and $k$, the size of $arr$ and the target value. 

The second line contains $n$ space-separated integers of the array $arr$.

Constraints

$2 \leq n \leq 10^5$  
$0 < k < 10^9$  
$0<arr[i]<2^{31}-1$    
each integer $\boldsymbol{arr}[i]$ will be unique

Sample Input
STDIN       Function
-----       --------
5 2         arr[] size n = 5, k =2
1 5 3 4 2   arr = [1, 5, 3, 4, 2]
    
Sample Output
3

Explanation

There are 3 pairs of integers in the set with a difference of 2: [5,3], [4,2] and [3,1]. .