huffman mintree

dynamicprogramming/java/src/com/com/brainbaking/greedy/Huffman.java

@@ -0,0 +1,72 @@
+package com.com.brainbaking.greedy;
+
+import java.util.*;
+import java.util.stream.Collectors;
+
+public class Huffman {
+
+    private final String toEncode;
+    private final Node root;
+
+    public Huffman(String toEncode) {
+        this.toEncode = toEncode;
+
+        root = buildMinRoot(buildQueue());
+    }
+
+    private Node buildMinRoot(Queue<Node> nodes) {
+        Node root = null;
+
+        while(nodes.size() > 1) {
+            Node first = nodes.poll();
+            Node second = nodes.poll();
+
+            root = new Node(first, second);
+            nodes.add(root);
+        }
+
+        // in geval van maar 1 karakter
+        return root == null ? nodes.poll() : root;
+    }
+
+    private Queue<Node> buildQueue() {
+        Set<Integer> chars = buildCharSet();
+        Queue<Node> tree = new PriorityQueue<>();
+
+        for(Integer character : chars) {
+            int frequency = (int) toEncode.chars().filter(c -> c == character).count();
+            tree.add(new Node(character, frequency));
+        }
+        return tree;
+    }
+
+    private Set<Integer> buildCharSet() {
+        return toEncode.chars().boxed().collect(Collectors.toSet());
+    }
+
+    public String encode() {
+        Map<Character, String> encodeMap = new HashMap<>();
+        buildEncodedMap(root, encodeMap, "");
+
+        String encoded = "";
+        for(int i = 0; i < toEncode.length(); i++) {
+            encoded += encodeMap.get(toEncode.charAt(i));
+        }
+        return encoded;
+
+        // wat is hier mis mee?
+        //return toEncode.chars().mapToObj(c -> encodeMap.get(c)).collect(Collectors.joining());
+    }
+
+    private void buildEncodedMap(Node node, Map<Character,String> map, String encoded) {
+        if(node.isRoot()) {
+            // in geval van maar 1 karakter
+            map.put(node.getCharacter(), encoded.equals("") ? "0" : encoded);
+            return;
+        }
+
+        buildEncodedMap(node.getLeft(), map, encoded + "0");
+        buildEncodedMap(node.getRight(), map, encoded + "1");
+    }
+
+}

dynamicprogramming/java/src/com/com/brainbaking/greedy/Node.java

@@ -0,0 +1,47 @@
+package com.com.brainbaking.greedy;
+
+public class Node implements Comparable<Node> {
+
+    private final char character;
+    private final int frequency;
+
+    private Node left;
+    private Node right;
+
+    public boolean isRoot() {
+        return left == null && right == null;
+    }
+
+    public Node getLeft() {
+        return left;
+    }
+
+    public Node getRight() {
+        return right;
+    }
+
+    public char getCharacter() {
+        return character;
+    }
+
+    public int getFrequency() {
+        return frequency;
+    }
+
+    public Node(Node left, Node right) {
+        this.left = left;
+        this.right = right;
+        this.character = '-';
+        this.frequency = left.getFrequency() + right.getFrequency();
+    }
+
+    public Node(Integer character, int frequency) {
+        this.character = (char) character.intValue();
+        this.frequency = frequency;
+    }
+
+    @Override
+    public int compareTo(Node o) {
+        return frequency - o.frequency;
+    }
+}

dynamicprogramming/java/test/com/brainbaking/greedy/HuffmanTest.java

@@ -0,0 +1,36 @@
+package com.brainbaking.greedy;
+
+import com.com.brainbaking.greedy.Huffman;
+import org.junit.Test;
+
+import static junit.framework.TestCase.assertEquals;
+
+public class HuffmanTest {
+
+    @Test
+    public void huffman_OnlyOnCharacter() {
+        Huffman huffman = new Huffman("aaa");
+
+        String result = huffman.encode();
+
+        assertEquals("000", result);
+    }
+
+    @Test
+    public void huffman_charAFrequences5TimesButBAndCOnlyOnce() {
+        Huffman huffman = new Huffman("baaaaac");
+
+        String result = huffman.encode();
+
+        assertEquals("001111101", result);
+    }
+
+    @Test
+    public void huffmanEncoded() {
+        Huffman huffman = new Huffman("hallo dit is een test wasda jong");
+
+        String result = huffman.encode();
+
+        assertEquals("110001101100110011000111101110100101111010000111001001011011101000100001011111001110100010111101111011111000011001110", result);
+    }
+}