Prefix Sum: Beginner

Welcome to my algorithmic journey! If you’ve ever looked at a coding challenge and felt like you were staring at a brick wall, you aren’t alone. Most of the time, the secret isn’t about being a math genius, it’s about recognising the pattern. In this series, we are breaking down the most essential coding patterns from beginner to expert level, keeping things simple, practical, and (hopefully) a little bit fun. Today, we are diving deep into Prefix Sum. Whether you are preparing for a big interview or just trying to write cleaner, faster code, mastering this pattern is a total game-changer. Let’s strip away the jargon and see how it actually works! What is Prefix Sum? Imagine you are standing at the start of a long road, and every mile there is a sign telling you how many coins are buried under the ground at that specific spot. If I asked you, “How many coins are there between mile 3 and mile 8?”, you would normally have to walk from 3 to 8 and add them up one by one. That works for a s