This talk describes three of the most beautiful pieces of code that I have ever written: three different implementations of Hoare's classic Quicksort algorithm.
# The first implementation is a bare-bones function in about a dozen lines of C.
# The second implementation starts by instrumenting the first program to measure its run time; a dozen systematic code transformations proceed to make it more and more powerful yet more and more simple, until it finally disappears in a puff of mathematical smoke. It therefore becomes the most beautiful program I never wrote.
# The third program is an industrial-strength C library Qsort function that I built with Doug McIlroy. A theme running through all three implementations is the power of elegance and simplicity.
(This talk expands my Chapter 3 in Beautiful Code, edited by Oram and Wilson and published by O'Reilly in July, 2007.)