Interview Questions

BFS explores level by level using a queue — best for shortest path in unweighted graphs. DFS goes as deep as possible using a stack/recursion — useful for topological sort, cycle detection, and exploring all paths. Both are O(V+E).

Use Floyd's tortoise-and-hare: advance one pointer by 1 and another by 2 each step. If they ever meet, there's a cycle; if the fast pointer reaches null, there isn't. O(n) time, O(1) space.

Normalization organizes tables to reduce redundancy and avoid update anomalies, via normal forms (1NF–3NF/BCNF). It improves data integrity but can require more joins; denormalization is sometimes used for read performance.

Atomicity (all-or-nothing transactions), Consistency (valid state transitions), Isolation (concurrent transactions don't interfere), Durability (committed data survives crashes). They guarantee reliable transaction processing in relational databases.

Event delegation attaches a single listener to a common ancestor instead of many listeners on individual children. Events bubble up, and you inspect `event.target` to act on the originating element. It reduces memory use and works for dynamically-added elements.

A closure is a function bundled with references to its surrounding lexical scope, retaining access to those variables after the outer function returns. Practical uses: data privacy (module pattern), function factories, and maintaining state in callbacks.

A process is an independent program with its own memory space; threads are lighter units of execution that share their process's memory. Threads are cheaper to create and communicate, but shared memory requires synchronization to avoid race conditions.

A decorator is a callable that wraps another function to extend its behavior without modifying it, applied with `@decorator` syntax. Common uses: logging, timing, caching (`functools.lru_cache`), access control. They are functions returning functions.

Vertical scaling adds more power (CPU/RAM) to one machine — simple but capped and a single point of failure. Horizontal scaling adds more machines — more complex (load balancing, data partitioning) but elastic and fault-tolerant.

DNS resolves the domain to an IP, a TCP (and TLS for HTTPS) connection is established, the browser sends an HTTP request, the server responds with HTML, then the browser parses HTML/CSS/JS, builds the DOM/CSSOM, and renders — fetching additional assets as needed.