# 1497. Check If Array Pairs Are Divisible by k

<https://leetcode.com/problems/check-if-array-pairs-are-divisible-by-k>

## Description

Given an array of integers `arr` of even length `n` and an integer `k`.

We want to divide the array into exactly `n / 2` pairs such that the sum of each pair is divisible by `k`.

Return *True* If you can find a way to do that or *False* otherwise.

**Example 1:**

```
**Input:** arr = [1,2,3,4,5,10,6,7,8,9], k = 5
**Output:** true
**Explanation:** Pairs are (1,9),(2,8),(3,7),(4,6) and (5,10).
```

**Example 2:**

```
**Input:** arr = [1,2,3,4,5,6], k = 7
**Output:** true
**Explanation:** Pairs are (1,6),(2,5) and(3,4).
```

**Example 3:**

```
**Input:** arr = [1,2,3,4,5,6], k = 10
**Output:** false
**Explanation:** You can try all possible pairs to see that there is no way to divide arr into 3 pairs each with sum divisible by 10.
```

**Example 4:**

```
**Input:** arr = [-10,10], k = 2
**Output:** true
```

**Example 5:**

```
**Input:** arr = [-1,1,-2,2,-3,3,-4,4], k = 3
**Output:** true
```

**Constraints:**

* `arr.length == n`
* `1 <= n <= 105`
* `n` is even.
* `-109 <= arr[i] <= 109`
* `1 <= k <= 105`

## ac

```java
```