Java 实现Huffman 编码算法

 
static class Tree {
                private Node root;
  
                public Node getRoot() {
                        return root;
                }
  
                public void setRoot(Node root) {
                        this.root = root;
                }
        }
  
        static class Node implements Comparable {
                private String chars = "";
                private int frequence = 0;
                private Node parent;
                private Node leftNode;
                private Node rightNode;
  
                @Override
                public int compareTo(Node n) {
                        return frequence - n.frequence;
                }
  
                public boolean isLeaf() {
                        return chars.length() == 1;
                }
  
                public boolean isRoot() {
                        return parent == null;
                }
  
                public boolean isLeftChild() {
                        return parent != null && this == parent.leftNode;
                }
  
                public int getFrequence() {
                        return frequence;
                }
  
                public void setFrequence(int frequence) {
                        this.frequence = frequence;
                }
  
                public String getChars() {
                        return chars;
                }
  
                public void setChars(String chars) {
                        this.chars = chars;
                }
  
                public Node getParent() {
                        return parent;
                }
  
                public void setParent(Node parent) {
                        this.parent = parent;
                }
  
                public Node getLeftNode() {
                        return leftNode;
                }
  
                public void setLeftNode(Node leftNode) {
                        this.leftNode = leftNode;
                }
  
                public Node getRightNode() {
                        return rightNode;
                }
  
                public void setRightNode(Node rightNode) {
                        this.rightNode = rightNode;
                }
        }
  
  
统计方法实现如下：
public static Map<Character, Integer> statistics(char[] charArray) {
                Map<Character, Integer> map = new HashMap<Character, Integer>();
                for (char c : charArray) {
                        Character character = new Character(c);
                        if (map.containsKey(character)) {
                                map.put(character, map.get(character) + 1);
                        } else {
                                map.put(character, 1);
                        }
                }
  
                return map;
        }
  
  
构建树
private static Tree buildTree(Map<Character, Integer> statistics,
                        List leafs) {
                Character[] keys = statistics.keySet().toArray(new Character[0]);
  
                PriorityQueue priorityQueue = new PriorityQueue();
                for (Character character : keys) {
                        Node node = new Node();
                        node.chars = character.toString();
                        node.frequence = statistics.get(character);
                        priorityQueue.add(node);
                        leafs.add(node);
                }
  
                int size = priorityQueue.size();
                for (int i = 1; i <= size - 1; i++) {
                        Node node1 = priorityQueue.poll();
                        Node node2 = priorityQueue.poll();
  
                        Node sumNode = new Node();
                        sumNode.chars = node1.chars + node2.chars;
                        sumNode.frequence = node1.frequence + node2.frequence;
  
                        sumNode.leftNode = node1;
                        sumNode.rightNode = node2;
  
                        node1.parent = sumNode;
                        node2.parent = sumNode;
  
                        priorityQueue.add(sumNode);
                }
  
                Tree tree = new Tree();
                tree.root = priorityQueue.poll();
                return tree;
        }
  
  
  
编码
public static String encode(String originalStr,
                        Map<Character, Integer> statistics) {
                if (originalStr == null || originalStr.equals("")) {
                        return "";
                }
  
                char[] charArray = originalStr.toCharArray();
                List leafNodes = new ArrayList();
                buildTree(statistics, leafNodes);
                Map<Character, String> encodInfo = buildEncodingInfo(leafNodes);
  
                StringBuffer buffer = new StringBuffer();
                for (char c : charArray) {
                        Character character = new Character(c);
                        buffer.append(encodInfo.get(character));
                }
  
                return buffer.toString();
        }
  
private static Map<Character, String> buildEncodingInfo(List leafNodes) {
                Map<Character, String> codewords = new HashMap<Character, String>();
                for (Node leafNode : leafNodes) {
                        Character character = new Character(leafNode.getChars().charAt(0));
                        String codeword = "";
                        Node currentNode = leafNode;
  
                        do {
                                if (currentNode.isLeftChild()) {
                                        codeword = "0" + codeword;
                                } else {
                                        codeword = "1" + codeword;
                                }
  
                                currentNode = currentNode.parent;
                        } while (currentNode.parent != null);
  
                        codewords.put(character, codeword);
                }
  
                return codewords;
        }
  
解码
public static String decode(String binaryStr,
                        Map<Character, Integer> statistics) {
                if (binaryStr == null || binaryStr.equals("")) {
                        return "";
                }
  
                char[] binaryCharArray = binaryStr.toCharArray();
                LinkedList binaryList = new LinkedList();
                int size = binaryCharArray.length;
                for (int i = 0; i < size; i++) {
                        binaryList.addLast(new Character(binaryCharArray[i]));
                }
  
                List leafNodes = new ArrayList();
                Tree tree = buildTree(statistics, leafNodes);
  
                StringBuffer buffer = new StringBuffer();
  
                while (binaryList.size() > 0) {
                        Node node = tree.root;
  
                        do {
                                Character c = binaryList.removeFirst();
                                if (c.charValue() == '0') {
                                        node = node.leftNode;
                                } else {
                                        node = node.rightNode;
                                }
                        } while (!node.isLeaf());
  
                        buffer.append(node.chars);
                }
  
                return buffer.toString();
        }
  
  
测试以及比较
  
public static void main(String[] args) {
                String oriStr = "Huffman codes compress data very effectively: savings of 20% to 90% are typical, "
                                + "depending on the characteristics of the data being compressed. 中华崛起";
                Map<Character, Integer> statistics = statistics(oriStr.toCharArray());
                String encodedBinariStr = encode(oriStr, statistics);
                String decodedStr = decode(encodedBinariStr, statistics);
  
                System.out.println("Original sstring: " + oriStr);
                System.out.println("Huffman encoed binary string: " + encodedBinariStr);
                System.out.println("decoded string from binariy string: " + decodedStr);
  
                System.out.println("binary string of UTF-8: "
                                + getStringOfByte(oriStr, Charset.forName("UTF-8")));
                System.out.println("binary string of UTF-16: "
                                + getStringOfByte(oriStr, Charset.forName("UTF-16")));
                System.out.println("binary string of US-ASCII: "
                                + getStringOfByte(oriStr, Charset.forName("US-ASCII")));
                System.out.println("binary string of GB2312: "
                                + getStringOfByte(oriStr, Charset.forName("GB2312")));
        }
  
        public static String getStringOfByte(String str, Charset charset) {
                if (str == null || str.equals("")) {
                        return "";
                }
  
                byte[] byteArray = str.getBytes(charset);
                int size = byteArray.length;
                StringBuffer buffer = new StringBuffer();
                for (int i = 0; i < size; i++) {                        byte temp = byteArray[i];                       buffer.append(getStringOfByte(temp));           }               return buffer.toString();       }       public static String getStringOfByte(byte b) {          StringBuffer buffer = new StringBuffer();               for (int i = 7; i >= 0; i--) {
                        byte temp = (byte) ((b >> i) & 0x1);
                        buffer.append(String.valueOf(temp));
                }
  
                return buffer.toString();
        }
 

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