/
huffman.rb
135 lines (112 loc) · 2.5 KB
/
huffman.rb
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class Node
attr_accessor :weight, :symbol, :left, :right, :parent
def initialize(params = {})
@weight = params[:weight] || 0
@symbol = params[:symbol] || ''
@left = params[:left] || nil
@right = params[:right] || nil
@parent = params[:parent] || nil
end
def walk(&block)
walk_node('', &block)
end
def walk_node(code, &block)
yield(self, code)
@left.walk_node(code + '0', &block) unless @left.nil?
@right.walk_node(code + '1', &block) unless @right.nil?
end
def leaf?
@symbol != ''
end
def internal?
@symbol == ''
end
def root?
internal? and @parent.nil?
end
end
class NodeQueue
attr_accessor :nodes, :huffman_root
def initialize(string)
frequencies = {}
string.each_char do |c|
frequencies[c] ||= 0
frequencies[c] += 1
end
@nodes = []
frequencies.each do |c, w|
@nodes << Node.new(:symbol => c, :weight => w)
end
generate_tree
end
def generate_tree
while @nodes.size > 1
sorted = @nodes.sort { |a,b| a.weight <=> b.weight }
to_merge = []
2.times { to_merge << sorted.shift }
sorted << merge_nodes(to_merge[0], to_merge[1])
@nodes = sorted
end
@huffman_root = @nodes.first
end
def merge_nodes(node1, node2)
left = node1.weight > node2.weight ? node2 : node1
right = left == node1 ? node2 : node1
node = Node.new(:weight => left.weight + right.weight, :left => left, :right => right)
left.parent = right.parent = node
node
end
end
class HuffmanEncoding
attr_accessor :root, :lookup, :input, :output
def initialize(input)
@input = input
@root = NodeQueue.new(input).huffman_root
@output = encode_string(input)
end
def lookup
return @lookup if @lookup
@lookup = {}
@root.walk do |node, code|
@lookup[code] = node.symbol if node.leaf?
end
@lookup
end
def encode(char)
self.lookup.invert[char]
end
def decode(code)
self.lookup[code]
end
def encode_string(string)
code = ''
string.each_char do |c|
code += encode(c)
end
code
end
def decode_string(code)
code = code.to_s
string = ''
subcode = ''
code.each_char do |bit|
subcode += bit
unless decode(subcode).nil?
string += decode(subcode)
subcode = ''
end
end
string
end
def to_s
@output
end
def [](char)
encode(char)
end
end
class String
def huffman
@huffman ||= HuffmanEncoding.new(self)
end
end