Techniques demonstrated:
- Solving an intractable problem using a scoring heuristic
- Super-indexing data structures for ultra-fast domain-specific queries
Summary (just gimme the TL;DR)
This is old-style artificial intelligence in action, solving within seconds a problem that would normally take eons to complete.
You give it a crossword grid, and a long list of words, and it finds ways to mesh words into the grid so as to form a complete crossword puzzle. The final working version was done in 2003 using C# version 1.2 with a minimalistic UI in WinForms.
The following 30-second video shows the crossword compiler in action, filling multiple successive crosswords using a word list taken from actual crosswords that have been published on the interwebz by various sources through the years. The video is in real time, showing that the crossword compiler is, in most cases, extremely fast.