Someone posted a question on comp.lang.ruby recently asking for help with solving anagrams. The poster originally asked about ways of generating permutations and several people pointed him to the facets library which has some permutation utility functions. As it turns out, I benchmarked the following naive permutation generator as 3 times faster than the facets library code:

def words chars, result='', &b
  if chars.empty?
    yield result
  else
    chars.length.times do |i|
      c = (x = chars.clone).slice!(i)
      words(x, result + c, &b)
    end
  end
end

However, generating all possible combinations of letters in an anagram is a very bad approach which doesn’t take into consideration key knowledge about the problem. Rather than generating all permutations of an anagram, which is infeasible for longer words, we can precompute a hash from our dictionary by using the sorted letters of words as keys. Then to solve an anagram, we simply sort the letters in the anagram and look it up in the hash.

The first program creates the hash and serializes it to disk for future anagram solving:

words = Hash.new([])

File.open("/usr/share/dict/words", "r") do |file|
  while line = file.gets
    word = line.chomp
    words[word.split('').sort!.join('')] += [word]
  end
end

File.open("word_hash", "w") do |file|
  Marshal.dump(words, file)
end

The second program loads the serialized hash from disk to solve anagrams that we type at the console:

words = nil

File.open("word_hash", "r") do |file|
  words = Marshal.load(file)
end

while true
  print "Enter word: "
  anagram = gets.chomp
  sorted_anagram = anagram.split('').sort!.join('')
  p  words[sorted_anagram]
end

This is really fast, but there are probably better methods. If you have one, feel free to add a comment with the code.