Check if array pairs are divisible by k

Array Hash Table Counting

46.2% acceptance

Feb 25, 2026

2617

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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.

Solution

Rust

Time O(n)

Space O(n)

LeetCode

solution.rs

impl Solution {
  pub fn can_arrange(arr: Vec<i32>, k: i32) -> bool {
    let k = k as i64;
    let mut cnt = vec![0i64; k as usize];
    for &x in &arr {
      let r = ((x as i64 % k) + k) % k;
      cnt[r as usize] += 1;
    }
    if cnt[0] % 2 != 0 { return false; }
    for r in 1..=(k / 2) as usize {
      if r == (k as usize - r) {
        if cnt[r] % 2 != 0 { return false; }
      } else if cnt[r] != cnt[k as usize - r] {
        return false;
      }
    }
    true
  }
}