10: java数据结构和算法: 构建哈夫曼树, 获取哈夫曼编码, 使用哈夫曼编码原理对文件压缩和解压

最终结果哈夫曼树,如图所示:

直接上代码:

public class HuffmanCode {
    public static void main(String[] args) {
        //获取哈夫曼树并显示
        Hnode root = createHuffmanTree(createNodes());
        root.beforePrint();
        System.out.println("====================");
        //从哈夫曼树中读取 哈夫曼编码
        getHuffmanCode(root);
        //从huffmanCodes 中读取哈夫曼编码:A:10, B:01, C:0011,D:11,E:000,F:00100,G:00101
        System.out.println("哈夫曼编码为:"+huffmanCodes);
    }

    //创建一个 Hnode节点的集合
    public static List<Hnode> createNodes(){
        List<Hnode> nodes = new ArrayList<Hnode>();
        nodes.add(new Hnode(new Person(12,"A"),60));
        nodes.add(new Hnode(new Person(13,"B"),45));
        nodes.add(new Hnode(new Person(14,"C"),13));
        nodes.add(new Hnode(new Person(15,"D"),69));
        nodes.add(new Hnode(new Person(16,"E"),14));
        nodes.add(new Hnode(new Person(17,"F"),5));
        nodes.add(new Hnode(new Person(18,"G"),3));
        return nodes;
    }
    //根据list 创建哈夫曼树
    public static Hnode createHuffmanTree(List<Hnode> nodes){
        while(nodes.size() > 1){
            //先对 nodes进行从小到大排序, 根据权重值进行从小到大排序
            Collections.sort(nodes, new Comparator<Hnode>() {
                public int compare(Hnode o1, Hnode o2) {
                    return o1.weight - o2.weight;
                }
            });
            //取出前二个最小的元素,构建一个父节点只有权重 没有数据的二叉树
            Hnode leftNode = nodes.get(0);
            Hnode rightNode = nodes.get(1);
            Hnode parent = new Hnode(null, leftNode.weight + rightNode.weight);
            parent.leftNode = leftNode;
            parent.rightNode = rightNode;

            //将原来nodes中已经处理的前二个最小元素删除调,并将parent节点存入nodes中
            nodes.remove(leftNode);
            nodes.remove(rightNode);
            nodes.add(parent);
        }
        //循环结束时候,nodes中只有一个节点了,且该节点就是哈夫曼树的根节点
        return nodes.get(0);
    }

    static StringBuilder stringBuilder = new StringBuilder();
    static Map<String,String> huffmanCodes = new HashMap<String, String>();
    //从哈夫曼树中读取 哈夫曼编码: A:10, B:01, C:0011,D:11,E:000,F:00100,G:00101
    public static void getHuffmanCode(Hnode root){
        if (root == null) {
            return ;
        }
        getCode(root.leftNode,"0",stringBuilder);
        getCode(root.rightNode,"1",stringBuilder);
    }

    private static void getCode(Hnode node, String code, StringBuilder builder) {
        StringBuilder builder1 = new StringBuilder(builder);
        builder1.append(code);
        if (node != null) {
            if (node.person == null) {
                //如果数据为不null,说明是子节点
                //左递归处理
                getCode(node.leftNode,"0",builder1);
                //右递归处理
                getCode(node.rightNode,"1",builder1);
            }else{
                //如果数据为null,说明是叶子节点
                huffmanCodes.put(node.person.name,builder1.toString());
            }
        }
    }
}

//先建节点
class Hnode{
    Person person;//数据
    int weight;//权重
    Hnode leftNode;
    Hnode rightNode;

    public Hnode(Person person, int weight) {
        this.person = person;
        this.weight = weight;
    }

    @Override
    public String toString() {
        return "Hnode{" +
                "data='" + person + '\'' +
                ", weight=" + weight +
                '}';
    }
    //前序遍历
    public void beforePrint(){
        System.out.println(this);
        if (this.leftNode != null) {
            this.leftNode.beforePrint();
        }
        if (this.rightNode != null) {
            this.rightNode.beforePrint();
        }
    }
}

class Person {
    int age;
    String name;

    public Person(int age, String name) {
        this.age = age;
        this.name = name;
    }

    @Override
    public String toString() {
        return "Person{" +
                "age=" + age +
                ", name='" + name + '\'' +
                '}';
    }
}

结果如下:

压缩原理:

1: 被压缩文件通过输入流,转化为原始字节数组, 遍历统计每个字节出现的次数,并转化为map, key:字节,value:该字节的次数

2: map 转化为list,根据list创建 哈夫曼树,并获取到对应的哈夫曼编码

3: 将哈夫曼编码转化字节数组,通过输出流,写入到目标文件中,同时将哈夫曼编码也写入到目标文件中(目的:是为了解码使用)

解压缩原理:

1: 通过输入流从被解压缩文件中,读取到哈夫曼编码,和 哈夫曼编码转化字节数组,

2: 解码 得到原始字节数组, 并将数组写出到目标文件中