Somewhat straddling pure cs and cryptography/coding theory: one of my absolute favorites: Merkle tree. It's used for easily confirming the integrity of data. E.

Somewhat straddling pure cs and cryptography/coding theory: one of my absolute favorites: Merkle tree. It's used for easily confirming the integrity of data. E.g. a filesystem. https://en.m.wikipedia.org/wiki/Merkle_tree https://en.m.wikipedia.org/wiki/Merkle_tree