1497. Check If Array Pairs Are Divisible by k

Problem Link

Description

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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.

 

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

Solution

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Python3

class Solution:
    def canArrange(self, arr: List[int], k: int) -> bool:
        count = [0] * k
 
        for x in arr:
            curr = x % k
            target = (k - curr) % k
 
            if count[target] > 0:
                count[target] -= 1
            else:
                count[curr] += 1
        
        return sum(count) == 0