On Computer Integrated Rationalized Crossword Puzzle Manufacturing

The crossword puzzle is a classic pastime that is well-known all over the world. We consider the crossword manufacturing process in more detail, investigating a two-step approach, first generating a mask, which is an empty crossword puzzle skeleton, and then filling the mask with words from a given dictionary to obtain a valid crossword. We show that the whole manufacturing process is NP-complete, and in particular also the second step of the two-step manufacturing, thus reproving in part a result of Lewis and Papadimitriou mentioned in Garey and Johnson’s monograph [M. R. Garey and D. S. Johnson. Computers and Intractability: A Guide to the Theory of NP-Completeness. W. H. Freeman and Company, 1979.] but now under real world crossword puzzle conditions. Moreover, we show how to generate high-quality masks via a memetic algorithm, which is used and tested in an industrial manufacturing environment, leading to very good results.