Data commit

Task/Huffman-coding/Ruby/huffman-coding.rb

@@ -0,0 +1,54 @@
+require 'priority_queue'
+
+def huffman_encoding(str)
+  char_count = Hash.new(0)
+  str.each_char {|c| char_count[c] += 1}
+
+  pq = CPriorityQueue.new
+  # chars with fewest count have highest priority
+  char_count.each {|char, count| pq.push(char, count)}
+
+  while pq.length > 1
+    key1, prio1 = pq.delete_min
+    key2, prio2 = pq.delete_min
+    pq.push([key1, key2], prio1 + prio2)
+  end
+
+  Hash[*generate_encoding(pq.min_key)]
+end
+
+def generate_encoding(ary, prefix="")
+  case ary
+  when Array
+    generate_encoding(ary[0], "#{prefix}0") + generate_encoding(ary[1], "#{prefix}1")
+  else
+    [ary, prefix]
+  end
+end
+
+def encode(str, encoding)
+  str.each_char.collect {|char| encoding[char]}.join
+end
+
+def decode(encoded, encoding)
+  rev_enc = encoding.invert
+  decoded = ""
+  pos = 0
+  while pos < encoded.length
+    key = ""
+    while rev_enc[key].nil?
+      key << encoded[pos]
+      pos += 1
+    end
+    decoded << rev_enc[key]
+  end
+  decoded
+end
+
+str = "this is an example for huffman encoding"
+encoding = huffman_encoding(str)
+encoding.to_a.sort.each {|x| p x}
+
+enc = encode(str, encoding)
+dec = decode(enc, encoding)
+puts "success!" if str == dec