"It's not enough to write code that works. Great engineers write code that works **well ." Why Does This Even Matter? Imagine you're building a contact search feature for a messaging app. You write the code, it works perfectly — on your laptop with 50 test contacts. Then the app launches. Users have 10,000 contacts. Search slows down. You get 50,000 users. The app crashes under load. The CEO is furious. The code was correct , but it wasn't efficient . This is exactly the problem that Time and Space Complexity helps us reason about — before we ship to a million users. Think of it like planning a road trip: Time Complexity = How long will the journey take? Space Complexity = How much luggage space do I need? Both matter. A trip that takes 2 hours is great. But if your car is so packed you can't breathe, that's a different problem.…