The Quest Begins (The "Why") I was grinding through a mock interview when the interviewer tossed me a problem: “Given an unsorted array, return the k‑th largest element.” My first instinct? Sort the whole thing and pick the element at index len‑k . Easy, right? But then I felt that nagging voice in the back of my head — “What if the array is huge? Sorting is O(n log n) and we only need one element.” I remembered a late‑night debugging session where I spent three hours staring at a timeo...