Algorithm for grouping anagram words

Question

Given a set of words, we need to find the anagram words and display each category alone using the best algorithm.

input:

man car kile arc none like
<         


        

Answer 1

I have implemented this before with a simple array of letter counts, e.g.:

unsigned char letter_frequency[26];

Then store that in a database table together with each word. Words that have the same letter frequency 'signature' are anagrams, and a simple SQL query then returns all anagrams of a word directly.

With some experimentation with a very large dictionary, I found no word that exceeded a frequency count of 9 for any letter, so the 'signature' can be represented as a string of numbers 0..9 (The size could be easily halved by packing into bytes as hex, and further reduced by binary encoding the number, but I didn't bother with any of this so far).

Here is a ruby function to compute the signature of a given word and store it into a Hash, while discarding duplicates. From the Hash I later build a SQL table:

def processword(word, downcase)
  word.chomp!
  word.squeeze!(" ") 
  word.chomp!(" ")
  if (downcase)
    word.downcase!
  end
  if ($dict[word]==nil) 
    stdword=word.downcase
    signature=$letters.collect {|letter| stdword.count(letter)}
    signature.each do |cnt|
      if (cnt>9)
        puts "Signature overflow:#{word}|#{signature}|#{cnt}"
      end
    end
    $dict[word]=[$wordid,signature]
    $wordid=$wordid+1
  end
end