974. Subarray Sums Divisible by K
https://leetcode.com/problems/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] <= 100002 <= K <= 10000
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| class Solution { | |
| public int subarraysDivByK(int[] A, int K) { | |
| int ans = 0, prefix = 0; | |
| int[] count = new int[K]; | |
| // If first element is multiple of K, count = 1 | |
| count[0] = 1; | |
| for (int num: A) { | |
| prefix = (prefix + num % K + K) % K; | |
| ans += count[prefix]++; | |
| } | |
| return ans; | |
| } | |
| } |
