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 <= A.length <= 30000
-10000 <= A[i] <= 10000
2 <= K <= 10000
Solution:
class Solution {
public int subarraysDivByK(int[] A, int K) {
int n = A.length;
Map<Integer, Integer> map = new HashMap();
map.put(0, 1);
int res = 0;
int prefixSum = 0;
for (int i = 0; i < n; i ++) {
int val = A[i];
prefixSum += val;
int mod = Math.floorMod(prefixSum, K);
// System.out.println(mod + ", " + map);
if (map.containsKey(mod)) {
res += map.get(mod);
}
map.put(mod, map.getOrDefault(mod, 0) + 1);
}
return res;
}
}