Norvig spell-check

Alphabet = ('a'..'z').to_a

NWORDS = begin
  words = Hash.new(0)
  File.read('big.txt').downcase.scan(/[a-z]+/).each { |w| words[w] += 1 }    
  words
end

def correct(word)
  (known([word]) || known(edits1(word)) || known_edits2(word) || [word]).max{|a,b| NWORDS[a] <=> NWORDS[b]}
end

def edits1(word)
  n = word.size
  (0..n).map do |i| 
    a, b = [word[0, i], word[i-n, n-i]]
    [ (a + b[1, n] unless b.empty?),
      (a + b[1, 1] + b[0, 1] + b[2, n] unless b.size < 2),
      (Alphabet.map { |c| a + c + b[1, n] } unless b.empty?),
      Alphabet.map { |c| a + c + b } ]
  end.flatten.uniq
end

def known_edits2(word)
  edits1(word).map { |e1| edits1(e1).select { |e2| NWORDS.has_key?(e2) } if e1 }.flatten
end
  
def known(words)
  list = words.select { |w| NWORDS.has_key?(w) }
  list.size > 0 ? list : false
end