Check If Array Pairs Are Divisible by k

Input: arr = [1,2,3,4,5,10,6,7,8,9], k = 5

Output: true

Pairs are (1,9), (2,8), (3,7), (4,6) and (5,10). Each pair sums to a multiple of 5.

Input: arr = [1,2,3,4,5,6], k = 7

Output: true

Pairs are (1,6), (2,5) and (3,4). Each pair sums to 7, which is divisible by 7.

Input: arr = [1,2,3,4,5,6], k = 10

Output: false

No way to divide arr into 3 pairs where each sum is divisible by 10.

Problem