Data structures your CS degree kind of glossed over

Hello, I'm Maneshwar. I'm building git-lrc, a Micro AI code reviewer that runs on every commit. It is free and source-available on Github. Star git-lrc to help devs discover the project. Do give it a try and share your feedback. Every CS program hammers the same seven into you. Arrays, linked lists, hash tables, stacks, queues, graphs, trees. You could probably recite their Big O complexities in your sleep at this point, and honestly, for 90% of the code you'll ever write, that's plenty. But every now and then a system hits a wall that none of the seven basics can handle gracefully, and someone had to invent a weirder tool to patch the gap. I went down a rabbit hole recently looking at a handful of these, and I liked them enough that I wanted to write them up properly instead of just leaving forty open tabs to rot. Fair warning, there is some depth here. Get a drink. When your hash table can't promise you a fast answer: Bloom filters Normal hash tables are great until you need to ask "have I possibly seen this before" across a dataset way too big to store in memory. Think a crawler checking billions of URLs, or a database deciding whether it's even worth going to disk to look for a row. A Bloom filter solves this by giving up on certainty in one direction. It's a fixed array of bits, plus a small handful of independent hash functions. Adding an item flips a handful of bits on. Checking for an item hashes it the same way and checks whether those same bits are on. If any single bit is off, that item was never added, full stop, no ambiguity. If they're all on, the item was probably added, but two unrelated items can accidentally light up the same bits, so you might get a false alarm. The asymmetry is the entire design. Zero false negatives, occasional false positives. It's the data structure equivalent of a metal detector at a stadium gate. It'll never wave through someone with a knife, but it might beep at your belt buckle and make you empty your pockets for nothing.