6.006 Introduction to Algorithms (Spring 2020, MIT OCW). Instructors: Prof. Erik Demaine, Dr. Jason Ku, and Prof. Justin Solomon. This course is an introduction to mathematical modeling of computational problems, as well as common algorithms, algorithmic paradigms, and data structures used to solve these problems. It emphasizes the relationship between algorithms and programming and introduces basic performance measures and analysis techniques for these problems.
(from ocw.mit.edu)
Lecture 19 - Complexity
Instructor: Prof. Erik Demaine. This lecture discusses computational complexity and introduces terminology: P, NP, EXP, R. These terms are applied to the concepts of hardness and completeness. The lecture ends with discussion on reductions.