Bitok & Plintus
Hey Plintus, ever wonder how the worst‑case for quicksort stretches out when you pick a really bad pivot? I’ve been chasing an edge case that seems to trip up the usual O(n²) analysis…
If you always pick the worst pivot—say the smallest or largest element—each partition splits into a 0‑sized side and an (n‑1)-sized side. Then the recurrence is T(n)=T(n‑1)+Θ(n), which telescopes to Θ(n²). That’s why randomized pivots or median‑of‑three are standard; they keep the expected split closer to n/2 and the average cost back to O(n log n). In short, a consistently bad pivot turns quicksort into a quadratic‑time nightmare.
That’s exactly what I was thinking—an evil pivot that always picks the extreme value turns every recursion into a straight‑line descent. It’s like playing a game of “find the smallest” over and over again, and the stack keeps getting taller, not shorter. I keep wondering if there’s a hidden constant that makes the worst case slightly less catastrophic, but until I find that constant, I’ll just stick to random picks and hope the universe doesn’t decide to be the devil’s advocate.
Sounds like you’re doing the math the same way you do training: run the numbers, spot the flaw, then throw a plan at it. If the universe keeps playing “devil’s advocate,” you’ll just be the one who keeps the clock ticking—no surprises. Keep the pivots random, or better yet, always pick the median of a few samples, and you’ll avoid that worst‑case trap. If you still want that hidden constant, run a profiling script; the constant is just the overhead of the partition loop, nothing that changes the n² nature. Stay disciplined, and you’ll never let the worst case catch you off‑guard.
Thanks for the pep talk—maybe if I just run the profiler on my own code, I’ll uncover the “hidden constant” and feel like I’m actually mastering quicksort, not just dodging its worst‑case. I’ll throw in a median‑of‑three pivot and see how long it takes to convince the universe that I’m not a math nerd who hates deadlines. Keep the code clean and the jokes dry, and we’ll keep the worst case at bay.