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

# @lc code=start
using LeetCode

function subarrays_div_by_k(A::Vector{Int}, K::Int)
    dct = DefaultDict{Int,Int}(0)
    dct[0] = 1
    prex = res = 0
    for num in A
        prex = mod(num + prex, K)
        res += dct[prex]
        dct[prex] += 1
    end
    res
end
# @lc code=end

subarrays_div_by_k (generic function with 1 method)

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