anagram.rb

def signature(word)
  word.downcase.chars.sort.join.intern
end

def build_anagrams(words)
  words.map { |word| [signature(word), word] }
       .inject({}) { |h, (sign, word)| h[sign] ||= []; h[sign] << word; h }
       .select { |sign, words| words.size > 1 }
end

def find_anagrams(word)
  sign = signature(word)
  res = Anagrams[sign]
  res ? res - [word] : []
end

def build_wordlist(path)
  File.open(path) do |f|
    f.map { |line| line.chomp.downcase }.uniq.reject { |word| word.size < 2 }
  end
end

WORDS = build_wordlist('/usr/share/dict/words')
Anagrams = build_anagrams(WORDS)

find_anagrams("name") # => ["amen", "enam", "mane", "mean", "nema"]
find_anagrams("tower") # => ["rowet", "wrote"]
find_anagrams("tester") # => ["retest", "setter", "street"]
find_anagrams("sister") # => ["resist", "restis"]
find_anagrams("friend") # => ["finder", "redfin", "refind"]