Problem

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 <= 10^5 n is even. -10^9 <= arr[i] <= 10^9 1 <= k <= 10^5

Pre analysis

Will mod all numbers with k and search for pairs.

Post analysis

The simple technique was to sum all integers and check if sum is divisible, since it was in pair

Another Solution

var canArrange = function(arr, k) {
    arr.reduce((a,c)=> a+c,0) % k === 0
};