Subarray Sum Divisible by K – Optimal Approach Using Prefix Sum + HashMap | C++, Java, Python

In this video, we solve the Subarray Sum Divisible by K problem and understand the intuition behind the optimized approach. Instead of checking every subarray, we use the prefix sum technique along with a HashMap to efficiently count the number of subarrays whose sum is divisible by K. In this video we cover: • Brute force intuition and why it is inefficient • Key observation using prefix sum • Why equal remainders help us find valid subarrays • How HashMap stores remainder frequencies • Clean implementation in C++, Java, and Python This problem is a very important extension of prefix sum concepts and is frequently asked in coding interviews. Rising Brain (DSA Sheet) - https://www.risingbrain.org/sheet Connect with me here: Linkedin -   / anjalikumari22   Instagram -   / rbanjali.codes   Twitter - https://x.com/anjali1kumari?s=21