Just another update

Task/Huffman-coding/Groovy/huffman-coding-1.groovy

@@ -0,0 +1,50 @@
+import groovy.transform.*
+
+@Canonical
+@Sortable(includes = ['freq', 'letter'])
+class Node {
+    String letter
+    int freq
+    Node left
+    Node right
+    boolean isLeaf() { left == null && right == null }
+}
+
+Map correspondance(Node n, Map corresp = [:], String prefix = '') {
+    if (n.isLeaf()) {
+        corresp[n.letter] = prefix ?: '0'
+    } else {
+        correspondance(n.left,  corresp, prefix + '0')
+        correspondance(n.right, corresp, prefix + '1')
+    }
+    return corresp
+}
+
+Map huffmanCode(String message) {
+    def queue = message.toList().countBy { it } // char frequencies
+        .collect { String letter, int freq ->   // transformed into tree nodes
+            new Node(letter, freq)
+        } as TreeSet // put in a queue that maintains ordering
+
+    while(queue.size() > 1) {
+        def (nodeLeft, nodeRight)  = [queue.pollFirst(), queue.pollFirst()]
+
+        queue << new Node(
+            freq:   nodeLeft.freq   + nodeRight.freq,
+            letter: nodeLeft.letter + nodeRight.letter,
+            left: nodeLeft, right: nodeRight
+        )
+    }
+
+    return correspondance(queue.pollFirst())
+}
+
+String encode(CharSequence msg, Map codeTable) {
+    msg.collect { codeTable[it] }.join()
+}
+
+String decode(String codedMsg, Map codeTable, String decoded = '') {
+    def pair = codeTable.find { k, v -> codedMsg.startsWith(v) }
+    pair ? pair.key + decode(codedMsg.substring(pair.value.size()), codeTable)
+         : decoded
+}

Task/Huffman-coding/Groovy/huffman-coding-2.groovy

@@ -0,0 +1,10 @@
+def message = "this is an example for huffman encoding"
+
+def codeTable = huffmanCode(message)
+codeTable.each { k, v -> println "$k: $v" }
+
+def encoded = encode(message, codeTable)
+println encoded
+
+def decoded = decode(encoded, codeTable)
+println decoded