Compresses a string using the literal approach to huffman encoding

huffman.rb

def freq_table(str)
  str.each_char.inject(Hash.new(0)) do |table, char|
    table[char] += 1
    table
  end.sort_by(&:last).reverse
end

def build_tree(freq_table)
  until freq_table.size == 1
    less_frequent = 2.times.map{ freq_table.pop }
    left, right = less_frequent
    new_node = [ 
      less_frequent.map(&:first).join(","), 
      left, right,
      less_frequent.map(&:last).inject(:+)
    ]
    freq_table.push new_node
  end
  freq_table.first
end

def draw_tree(tree)
  chars = tree.shift
  freq  = tree.pop
  left, right = tree
  label = %Q{"{#{chars.gsub(/\s+/, "_")}}:#{freq}"}
  if [left, right].all?(&:nil?)
    label 
  else
    "#{label}->#{draw_tree(left)};#{label}->#{draw_tree(right)}"
  end
end

def draw(dot)
  File.open("dotit", 'w') do |f|
    f.write("digraph{#{dot}}")
  end
  `dot -Tpng dotit -o dotted.png && open dotted.png`
end

def encode(table, tree, acum = "")
  chars = tree.shift
  freq  = tree.pop
  left, right = tree
  unless [left, right].all?(&:nil?)
    encode table, left, acum + "0"
    encode table, right, acum + "1"
  else
    table[chars] = acum
  end
end

def huffman_codes(tree)
  codes = {}
  encode(codes, tree)
  codes
end

def compress(str)
  tree = build_tree(freq_table(str))
  draw(draw_tree(tree))
  codes = huffman_codes(build_tree(freq_table(str)))
  puts "The huffman codes are: #{codes.inspect}"
  str.each_char.map do |char|
    codes[char]
  end.join("")
end

puts "The compressed string is", compress(ARGV.pop)