Fourth book in a series that provides an accessible, nononsense, and programming languageagnostic introduction to algorithms. Includes hints or solutions to all quizzes and problems, and a series of YouTube videos by the author accompanies the book. Part 4 covers algorithmic tools for tackling NPhard problems (heuristic algorithms, local search, dynamic programming, MIP and SAT solvers) and techniques for quickly recognizing NPhard problems in the wild.