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

Solution(javascript)

/**
 * @param {number[]} arr
 * @param {number} k
 * @return {boolean}
 */
const canArrange = function (arr, k) {
  const reminders = []
  for (const num of arr) {
    let current = num % k
    if (current < 0) {
      current += k
    }
    reminders[current] = (reminders[current] || 0) + 1
  }
  for (let i = 1; i < k; i++) {
    if (reminders[i] !== reminders[k - i]) {
      return false
    }
  }
  return (reminders[0] || 0) % 2 === 0
}