Barden's tool

bardens_tool.rb

dictionary = IO.readlines("path/to/your/dictionary").map {|word| word.chomp}

# you can replace "path/to/your/dictionary" with "/usr/share/dict/words", but I
# recommend a smaller dictionary, such as the one I've saved here: 
# https://github.com/pgblu/dryphtwords/blob/master/app/fixtures/main_dictionary.txt

needed_length = ARGV[0].to_i
dropped_letter = ARGV[1]

intermediate_result = dictionary.select {|word| word.length == needed_length && word.split('').include?(dropped_letter)}

def drop_letter(word, letter)
  ar = word.split('')
  droppables = ar.each_index.select {|ix| ar[ix] == letter}
  return droppables.map {|index| v = ar.dup; v.delete_at(index); v.join}
end

result = intermediate_result.select do |word|
  drop_letter(word, dropped_letter).any? do |new_word|
    dictionary.include? new_word
  end
end

result.map {|word| puts word}