Letterpress Word Finder

In an attempt to start to blog more, here's a quick follow-up post on the previous Letterpress article.

Background

As a reminder, here's how I outlined steps in creating a Letterpress solver:

1. Take screenshot of game and import it into solver
2. Parse the board into a string of letters
3. Reduce a dictionary of valid words against those characters to find playable words
4. Optionally make recommendations of which word to play based on current board state and strategy. (i.e. don't be naive)

We built step one (sort-of) and step two in the previous article, so let's move on to step three.

Requirements

We want our script to fulfill the following requirements:

1. Accept the board letters via STDIN or commandline arguments.
2. Reduce the dictionary words against those letters.
3. Dump out matching words (without regard to board state/strategy).

Implementation

We'll take either an argument or read STDIN and downcase it.

letters = (ARGV[0] || STDIN.read).downcase

I don't have the official Letterpress dictionary (a quick googling will get you on the right track if you insist), but every good unix-y system has a dictionary file.

$ cat /usr/share/dict/words | wc -l
235886

OK, that's a lot of words. Let's pull them in and downcase them too.

words = File.read("/usr/share/dict/words").downcase.split("\n")

Now, the only really interesting part: a method to determine if a word can be constructed from letters. I've shamelessly borrowed a perfectly fast solution from Stackoverflow.

def is_subset?(word, letters)
  !word.chars.find{|char| word.count(char) > letters.count(char)}
end

And now we reduce our words by those that match our letters

matching_words = words.select do |word|
  is_subset?(word, letters)
end

And there's nothing left to do but dump them out.

puts matching_words.sort_by(&:length)

Here's the entire word generating script.

And an example of using it with the board parser from the previous post:

$ ruby -r ./board_parser -e "puts BoardParser.new('light.png').tiles.join" | ruby letter.rb | tail -n 10
hermodactyl
typhlectomy
cryohydrate
polydactyle
pterodactyl
crymotherapy
hydrolyzable
acetylthymol
overthwartly
protractedly

Excellent. Of course, not all words in your system's dictionary file may be playable, YMMV, etc.