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 <= A.length <= 30000
-10000 <= A[i] <= 10000
2 <= K <= 10000
class Solution {
public int subarraysDivByK(int[] A, int K) {
// Map of Sum -> Frequency
HashMap<Integer, Integer> map = new HashMap<>();
map.put(0, 1);
int count = 0, sum = 0;
for (int x : A) {
sum = (sum + x);
int remainder = sum % K;
if (remainder < 0)
remainder += K; // Because -1 % 5 = -1, but we need the positive mod 4
count += map.getOrDefault(remainder, 0);
map.put(remainder, map.getOrDefault(remainder, 0) + 1);
}
return count;
}
}
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