Make words out of airport codes

airport_code_word_finder.rb

# https://twitter.com/xor/status/978793975590150144

require 'open-uri'
require 'csv'

class PrefixTreeSearch
  attr_reader :codes, :words, :root
  attr_accessor :found

  MAX_LENGTH = 12

  def initialize
    @codes = CSV.parse(
      open('http://ourairports.com/data/airports.csv'),
      headers: true,
    ).map do |row|
      case row['type']
      when 'large_airport', 'medium_airport'
        row['iata_code']
      else
        nil
      end
    end.uniq.compact.sort.select do |row|
      row =~ /^[A-Z]+$/
    end
    @words = open('/usr/share/dict/words').readlines.map(&:chomp).map(&:upcase)
    build_tree
    @found = []
  end

  def build_tree
    @root = Node.new(nil)
    words.each do |word|
      letters = word.split('')
      cursor = root
      letters.each do |letter|
        child = cursor.find_child(letter)
        if child.nil?
          child = Node.new(letter)
          cursor.children << child
        end
        cursor = child
      end
      cursor.terminal = true
    end
  end

  def is_word?(word)
    root.is_terminal_path?(word.split(''))
  end

  def is_partial_word?(word)
    root.is_path?(word.split(''))
  end

  def search(word = '')
    if is_word?(word)
      puts word
      found << word
    end
    return if word.size >= MAX_LENGTH || !is_partial_word?(word)

    codes.each do |code|
      search(word + code)
    end
  end

  class Node
    attr_reader :children, :value
    attr_accessor :terminal

    def initialize(value)
      @children = []
      @value = value
      @terminal = false
    end

    def find_child(value)
      children.find do |child|
        child.value == value
      end
    end

    def is_path?(values)
      cursor = self
      values.each do |value|
        cursor = cursor.find_child(value)
        return false if cursor.nil?
      end
      true
    end

    def is_terminal_path?(values)
      cursor = self
      values.each do |value|
        cursor = cursor.find_child(value)
        return false if cursor.nil?
      end
      return cursor.terminal
    end
  end
end

PrefixTreeSearch.search