# 2006. Count Number of Pairs With Absolute Difference K

<https://leetcode.com/problems/count-number-of-pairs-with-absolute-difference-k>

## Description

Given an integer array `nums` and an integer `k`, return *the number of pairs* `(i, j)` *where* `i < j` *such that* `|nums[i] - nums[j]| == k`.

The value of `|x|` is defined as:

* `x` if `x >= 0`.
* `-x` if `x < 0`.

**Example 1:**

```
**Input:** nums = [1,2,2,1], k = 1
**Output:** 4
**Explanation:** The pairs with an absolute difference of 1 are:
- [**1**,**2**,2,1]
- [**1**,2,**2**,1]
- [1,**2**,2,**1**]
- [1,2,**2**,**1**]
```

**Example 2:**

```
**Input:** nums = [1,3], k = 3
**Output:** 0
**Explanation:** There are no pairs with an absolute difference of 3.
```

**Example 3:**

```
**Input:** nums = [3,2,1,5,4], k = 2
**Output:** 3
**Explanation:** The pairs with an absolute difference of 2 are:
- [**3**,2,**1**,5,4]
- [**3**,2,1,**5**,4]
- [3,**2**,1,5,**4**]
```

**Constraints:**

* `1 <= nums.length <= 200`
* `1 <= nums[i] <= 100`
* `1 <= k <= 99`

## ac

```java
```