README.md

1497. Check If Array Pairs Are Divisible by k

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.

Constraints:

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

Solutions (Rust)

1. Solution

impl Solution {
    pub fn can_arrange(arr: Vec<i32>, k: i32) -> bool {
        let mut count = vec![0; k as usize];

        for &x in &arr {
            count[x.rem_euclid(k) as usize] += 1;
        }

        for i in 1..(k as usize + 1) / 2 {
            if count[i] != count[k as usize - i] {
                return false;
            }
        }

        k % 2 == 1 || count[k as usize / 2] % 2 == 0
    }
}