Hey Codeforces! Today I started learning the precomputation technique of prefix sum, covering both 1D and 2D arrays, as it’s a powerful tool for speeding up range queries. Since I’m new to this topic, I followed some lectures and made rough handwritten notes to better understand the concept—check them out here. Before moving on to other important topics like precomputation + hashing, basic modular arithmetic, and related number theory tricks, I want to practice 5–10 problems focused on prefix sums (range sum queries in 1D and submatrix sums in 2D). If you know any beginner to intermediate-level problems that helped you grasp prefix sums better, please drop them in the comments. Let’s keep learning and leveling up together! – algorider