Lab: think in systems

Scenarios: thinking in systems

1. 1.

   A function takes two numbers and returns their sum — no logging, no globals, no I/O. If you call it with the same inputs a thousand times, what happens?
   You always get the same result and nothing outside the function changesThe result may vary because the function is statefulThe function will eventually throw once the CPU warms upThe second call is cached by the runtime
2. 2.

   You change a low-level utility function and four unrelated modules break. The most likely cause is:
   High cohesionHigh couplingA pure functionGood abstraction
3. 3.

   You call db.findUser(id) without knowing whether the underlying storage is PostgreSQL, SQLite, or an in-memory map. This is an example of:
   A side effectTight couplingAn abstraction hiding implementation details behind a stable interfaceA performance anti-pattern
4. 4.

   Your code frequently checks whether a username already exists in a growing collection of thousands. Which structure gives the best performance?
   A list — scan from the beginning each timeA set — near-constant time membership checksA stack — last-in, first-outA string — join all names with commas and use indexOf
5. 5.

   A function loops over every item in a list of n items, and for each one loops over the list again. Its time complexity is roughly:
   O(1)O(n)O(n²)O(log n)