Twitter OA : K-Difference

Given an array of distinct integers and a target value, determine the number of distinct pairs of integers in the array with an absolute difference equal to the target amount. Two pairs are distinct if they differ in at least one value. To illustrate, the pairs (1, 3) and (3, 2) are distinct. The pairs (1, 3) and (3, 1) are not.
For example, given the array a = [1,3,5] and a target difference k = 2. There are two pairs: [1,3] and [3,5], that have the target difference.

Function Description
Complete the function kDifference in the editor below. The function must return an integer that represents the number of distinct pairs in a having a difference of k.
kDifference has the following parameter(s);
a[a[0]....a[n-1]]: array of integers
k: the target difference
Constraints
• 5 <= n <= 10^5
• 0 < a[i] <= 2 * 10^9
• Each a[i] is distinct, i.e. unique within a.
• 1 <= k <= 10^9

Sample Input :
[1, 5, 3, 4, 2, 2]

Sample Output :
3

Explanation
Count the number of pairs in a = [1,5, 3, 4, 2] whose difference is k = 2. The following three pairs meet the criterion: (1,3), (5, 3), and (4,2).

Sample Input :
[363374326,364147530,61825163,107306571,128124602,139946991,428047635,491595254,879792181,106926279]

Sample Output:
0

Explanation:
Count the number of pairs in a = [363374326, 364147530, 61825163, 107306571, 1281246024, 139946991, 428047635, 491595254, 879792181, 106926279] whose difference is k = 1. Because no such pair of integers exists in a, return 0.

Sample Input :
[6,2,4,6,8,10,12,2]

Sample Output :
5

Explanation:
Count the number of pairs in a = [2, 4, 6, 8, 10, 12] whose difference is k = 2. The following five pairs meet the criterion: (2,4),(4, 6), (6,8), (8, 10), and (10, 12).