hashing

A grounded systems-coding screen: find files with identical content across a tree. The naive all-pairs hash is wasteful. The signal is the size prefilter and a cheap-hash gate before the full hash. Here is the layered approach.

Rabin-Karp slides a fixed-width hash over the text so each window costs O(1) to update, making it ideal for matching many patterns at once. The signal is the polynomial rolling hash, modular arithmetic, and why you still verify on a hash hit. Here is the answer.

A deceptively rich warm-up. The interesting decisions are how you generate short, collision-free, unguessable keys at scale, and how a read-heavy 100:1 workload shapes the storage and caching. Here is the clean design with capacity math.