The Quest Begins (The "Why")


I still remember the first time I faced a problem that asked for the sum of numbers in a sub‑array, over and over again, with updates sprinkled in between. It felt like I was stuck in a never‑ending loop of for i in range(l, r+1): total += arr[i] – O(n) per query, and with up to 10⁵ queries the solution timed out...