- Trees and Binary Search Trees
The BST invariant and the O(log n) it buys — but only while the tree stays balanced, and inserting sorted data makes it a linked list in disguise. All four traversals, why in-order comes out sorted, and deletion with two children, the case everyone skips.
- Spring Boot – Retries
@Retryable with exponential backoff and a @Recover fallback, applied to the Stripe calls in the pizza API. Which exceptions are worth retrying and which just waste time, and the correctness rule underneath all of it: retrying a non-idempotent call is how you charge a customer twice.
- Python Advanced – Generators & Iterators
Past yield. The iterator protocol written out by hand, generators used as coroutines with send and throw, why contextlib turns one into a context manager, and the itertools functions worth knowing by name.
- Python – File (read/write)
Reading and writing files with `with open(...)`, why the context manager is not optional, reading a large file a line at a time, `pathlib` instead of string paths, and the CSV and JSON modules you will reach for straight afterwards.
- Frontend Dev – The HTML, CSS and Browser You Actually Need
The platform underneath every framework. What the browser does with your page — DOM, CSSOM, layout, paint — why semantic HTML decides what a screen reader and Google can see, and the small part of CSS that carries most real layouts: the box model, flexbox, grid, the cascade and custom properties.