This is a sudoku-solving program written as a literate programming document, using Org Mode and Org Babel. The C code in sudoku.c is entirely generated from sudoku.org through the Emacs command org-babel-tangle.
While the Org file can be read comfortably in GitHub’s default viewer, it was designed to be converted into a LaTeX document by the command org-latex-export-as-latex, and therefore includes some Org features not supported by GitHub, as well as some raw LaTeX commands.