Leetcode Problem 974. Subarray Sums Divisible by K

974. Subarray Sums Divisible by K

Leetcode Solutions

Key approach of the solution: Prefix Sums and Counting Remainders

  1. Initialize result to 0, to store the count of subarrays divisible by k.
  2. Initialize prefixMod to 0, to store the current prefix sum modulo k.
  3. Initialize an array modGroups of size k to store the count of prefix sums for each possible modulo value. Set modGroups[0] to 1.
  4. Iterate over the elements of nums. a. Update prefixMod with the current element's contribution: (prefixMod + nums[i] % k + k) % k. b. Add modGroups[prefixMod] to result, since this is the number of subarrays ending at the current index with a sum divisible by k. c. Increment modGroups[prefixMod] by 1.
  5. Return result.
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Alternative approach: Brute Force

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