Three Instead of Four: Recursion and Divide and Conquer

Deep End Era. Engineering with Sankalp · Oct 28, 2026 · 53m

A payments app takes two seconds to sign each transaction on a cheap phone, and the intern who profiles it says schoolbook multiplication is "the only way to multiply". In 1960, Andrey Kolmogorov thought so too, until a 23-year-old student proved him wrong in a week. Part four of The Deep End's algorithms series explains recursion and divide and conquer: how to trust a recursive algorithm, how to read its cost with the master theorem, and how Karatsuba, Strassen and the closest-pair algorithm did what seemed impossible, up to DeepMind's AlphaTensor and the 2019 n log n multiplication result…