Microsoft has open source’d GW BASIC, originally released in 1983. You can browse the source here on GitHub, but the article looking back at what was also going in in tech in 1983 is also a fascinating look back in history.
Sudoku and Exact Cover problems
Sudoku is an example of an Exact Cover problem and can be solved by picking a subset of candidate rows from the exact cover matrix that satisfy all of the constraints for the complete grid.
I explored building an implementation of Donald Knuth’s Algorithm X using Dancing Links as a Sudoku solver, which you can read more about here.
For a 9×9 Sudoku puzzle, a candidate grid has x possible candidates, by y constraints.
For a 9×9 grid using numbers 1 through 9, there are:
9 rows x 9 columns x 9 (values 1 through 9) = 729
… possible candidate values for the cells.
For 4 constraints applied to every cell in the 9×9 grid, there are
9 rows x 9 columns x 4 constraints = 324
… constraints to be met.
If you fill a grid where a 1 represents a met constraint by that candidate and 0 is unmet, if you zoom out far enough the table looks like this:
To see how a matrix like this is used together with Donald Knuth’s Algorithm X and Dancing Links, see my previous post here.
Upgrading cmake on Raspbian Jessie
Trying to build and install rtl-sdr from source I got this error on a Raspberry Pi 1 running Jessie:
$ cmake ../
CMake Error at CMakeLists.txt:22 (cmake_minimum_required): CMake 3.7.2 or higher is required. You are running version 3.6.2
Doing an ‘apt-get update’ and ‘apt-get upgrade’ is not picking up a more recent version, so following the steps here, I downloaded the required 3.7.2 version from source and followed the steps to build it: http://osdevlab.blogspot.com/2015/12/how-to-install-latest-cmake-for.html
I downloaded a .tar for the 3.7.2 version from:
The build look over 2 hours, but completed successfully, and now I’m able to build rtl-sdr.
Java Report magazine September 2000
