gistfile1.rb

module Abbrev

  # Given a set of strings, calculate the set of unambiguous
  # abbreviations for those strings, and return a hash where the keys
  # are all the possible abbreviations and the values are the full
  # strings. Thus, given input of "car" and "cone", the keys pointing
  # to "car" would be "ca" and "car", while those pointing to "cone"
  # would be "co", "con", and "cone".
  #
  # The optional +pattern+ parameter is a pattern or a string. Only
  # those input strings matching the pattern, or begging the string,
  # are considered for inclusion in the output hash

  def abbrev(words, pattern = nil)
    table = {}
    seen = Hash.new(0)

    if pattern.is_a?(String)
      pattern = /^#{Regexp.quote(pattern)}/	# regard as a prefix
    end

    words.each do |word|
      next if (abbrev = word).empty?
      while (len = abbrev.rindex(/[\w\W]\z/)) > 0
	abbrev = word[0,len]

	next if pattern && pattern !~ abbrev

	case seen[abbrev] += 1
	when 1
	  table[abbrev] = word
	when 2
	  table.delete(abbrev)
	else
	  break
	end
      end
    end

    words.each do |word|
      next if pattern && pattern !~ word

      table[word] = word
    end

    table
  end

  module_function :abbrev
end