LeetCode 974. Subarray Sums Divisible by K

Question

Given an integer array nums and an integer k, return the number of non-empty subarrays that have a sum divisible by k.

A subarray is a contiguous part of an array.

https://leetcode.com/problems/subarray-sums-divisible-by-k/

• Solution1

class Solution {
    public int subarraysDivByK(int[] A, int K) {
        Map<Integer, Integer> map = new HashMap<>();
        map.put(0, 1);
        int count = 0, sum = 0;
        for(int a : A) {
            sum = (sum + a) % K;
            if(sum < 0) sum += K;  // Because -1 % 5 = -1, but we need the positive mod 4
            count += map.getOrDefault(sum, 0);
            map.put(sum, map.getOrDefault(sum, 0) + 1);
        }
        return count;
    }
}

Complexity:

Time complexity: O( n)

Space complexity: O(n)