Problem Brief

Counting Pairs

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Given an integer k and a list of integers, count the number of distinct valid pairs of integers (a, b) in the list for which a + k = b. Two pairs of integers (a, b) and (c, d) are considered distinct if at least one element of (a, b) does not also belong to (c, d). Note that the elements in a pair might be the same element in the array. An instance of this is below where k = 0.

Function Description

Complete the function countPairs in the editor.

countPairs has the following parameter(s):

int numbers[n]: array of integers
int k: target difference

Returns

int: number of valid (a, b) pairs in the numbers array that have a difference of k

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1Example 1

Input

numbers = [1, 1, 1, 2], k = 1

Output

Explanation

This arr has 3 different valid pairs: (1, 1), (1, 2), and (2, 2,). For k = 1, there is only 1 valid pair which satisfies a + k = b: the pair (a, b) = (1, 2)

2Example 2

Input

numbers = [1, 2], k = 0

Output

Explanation

This arr has 3 different valid pairs: (1, 1), (1, 2), and (2, 2,). For k = 0, there is only 2 valid pair which satisfies a + k = b: 1 + 0 = 1 and 2 + 0 = 2.

Constraints

Limits and guarantees your solution can rely on.

2 <= n <= 2 * 10^5

0 <= numbers[i] <= 10^9, where 0 <= i < n

0 <= k <= 10^9