LeetCode [974] Subarray Sums Divisible by K

Given an array A of integers, return the number of (contiguous, non-empty) subarrays that have a sum divisible by K.

 

Example 1:

Input: A = [4,5,0,-2,-3,1], K = 5
Output: 7
Explanation: There are 7 subarrays with a sum divisible by K = 5:
[4, 5, 0, -2, -3, 1], [5], [5, 0], [5, 0, -2, -3], [0], [0, -2, -3], [-2, -3]

 

Note:

1. 1 <= A.length <= 30000
2. -10000 <= A[i] <= 10000
3. 2 <= K <= 10000

class Solution {
    public int subarraysDivByK(int[] A, int K) {
        int n = A.length;
        int sum = 0;
        int ret = 0;
        Map<Integer, Integer> map = new HashMap<>();
        map.put(0, 1);
        for(int i=0; i<n; ++i){
            sum += A[i];
            int m = sum%K;
            if(m<0) m += K;
            if(map.containsKey(m)){
                ret += map.get(m);
            }
            map.put(m, map.getOrDefault(m, 0)+1);
        }
        return ret;
    }
}