The Quest Begins (The “Why”) I still remember the first time I stared at a binary tree problem and felt my brain short‑circuit. The prompt asked me to compute the sum of all node values. I’d written a neat little for loop for arrays before, but trees? They don’t come in neat rows. My first instinct was to slap a while loop on a stack, push nodes, pop them, and keep a running total. It worked… sort of. The code was a tangled mess of manual bookkeeping, and every time I tweaked the tree sh...