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Tested Python solution for LeetCode 974 with 12 pytest cases. Generate a practice environment with lcpy.
lcpy gen -n 974 # by problem number
lcpy gen -s subarray_sums_divisible_by_k # by problem name
nums and an integer k, return the number of non-empty subarrays that have a sum divisible by k.
A subarray is a contiguous part of an array.
Input: nums = [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]
Input: nums = [5], k = 9
Output: 0
1 <= nums.length <= 3 * 10^4-10^4 <= nums[i] <= 10^42 <= k <= 10^4class Solution:
# Time: O(n)
# Space: O(k)
def subarrays_div_by_k(self, nums: list[int], k: int) -> int:
mod_count: dict[int, int] = {0: 1}
prefix_mod = 0
count = 0
for num in nums:
prefix_mod = (prefix_mod + num) % k
count += mod_count.get(prefix_mod, 0)
mod_count[prefix_mod] = mod_count.get(prefix_mod, 0) + 1
return count
| Time | Space |
|---|---|
| O(n) | O(k) |