java实现哈夫曼编码

哈夫曼算法

众所周知，哈夫曼算法适用于文件压缩领域。由于上机需要，就写了一个Java代码实现。

哈夫曼算法的内容

1.将带有符号的字母存储为叶子节点，其权值为符号出现的次数
2.从这些叶子结点中找到权值最小的两个节点，然后将其合并成一个新节点，即新节点的权值为两个节点的权值之和，然后删除这两个节点。
3.将新节点加入队列中。重复2-3步骤直到队列只有一个节点。

哈夫曼的实现

1.定义TreeNode节点

private static class TreeNode implements Comparable<TreeNode>{        TreeNode left;        TreeNode right;        int weight;        char ch;        String code;        public TreeNode(int weight,TreeNode left,TreeNode right) {            this.weight = weight;            this.left = left;            this.right = right;            this.code = "";        }        @Override        public int compareTo(TreeNode o) {            if (this.weight > o.weight) {                return 1;            }else if (this.weight < o.weight) {                return -1;            }else {                return 0;            }           }    }

ch保存相应字符。code保存0或1，方便打印字符编码。

2.实现核心算法
这里用了一个TreeSet的容器装节点，因为它自带排序功能。（前提是对象为Comparable的子类）

public static TreeNode huffman(TreeMap<Integer, Character> data) {        TreeSet<TreeNode> tNodes = new TreeSet<>();        Set<Integer> weights = data.keySet();        Iterator<Integer> iterator = weights.iterator();        while (iterator.hasNext()) {            int weight = iterator.next();            TreeNode tmp = new TreeNode(weight, null, null);            tmp.ch = data.get(weight);            tNodes.add(tmp);        }        while (tNodes.size() > 1) {            TreeNode leftNode = tNodes.pollFirst();            leftNode.code = "0";            TreeNode rightNode = tNodes.pollFirst();            rightNode.code = "1";            TreeNode newNode = new TreeNode(leftNode.weight+rightNode.weight,                    leftNode, rightNode);            tNodes.add(newNode);        }        return tNodes.first();    }

3.得到字符编码

private static void code(TreeNode t) {        if (t.left != null) {            t.left.code = t.code + t.left.code;            code(t.left);        }        if (t.right != null) {            t.right.code = t.code + t.right.code;            code(t.right);        }    }

4.打印字符编码结果

public static void print(TreeNode root) {        if (root != null) {            if (root.left == null && root.right == null) {                System.out.println(root.ch + " 编码：" + root.code);            }else {                print(root.left);                print(root.right);            }        }    }

结果截图

最后放上完整代码：

import java.util.Iterator;import java.util.Set;import java.util.TreeMap;import java.util.TreeSet;public class Huffman {    private static class TreeNode implements Comparable<TreeNode>{        TreeNode left;        TreeNode right;        int weight;        char ch;        String code;        public TreeNode(int weight,TreeNode left,TreeNode right) {            this.weight = weight;            this.left = left;            this.right = right;            this.code = "";        }        @Override        public int compareTo(TreeNode o) {            if (this.weight > o.weight) {                return 1;            }else if (this.weight < o.weight) {                return -1;            }else {                return 0;            }           }    }    public static TreeNode huffman(TreeMap<Integer, Character> data) {        TreeSet<TreeNode> tNodes = new TreeSet<>();        Set<Integer> weights = data.keySet();        Iterator<Integer> iterator = weights.iterator();        while (iterator.hasNext()) {            int weight = iterator.next();            TreeNode tmp = new TreeNode(weight, null, null);            tmp.ch = data.get(weight);            tNodes.add(tmp);        }        while (tNodes.size() > 1) {            TreeNode leftNode = tNodes.pollFirst();            leftNode.code = "0";            TreeNode rightNode = tNodes.pollFirst();            rightNode.code = "1";            TreeNode newNode = new TreeNode(leftNode.weight+rightNode.weight,                    leftNode, rightNode);            tNodes.add(newNode);        }        return tNodes.first();    }    private static void code(TreeNode t) {        if (t.left != null) {            t.left.code = t.code + t.left.code;            code(t.left);        }        if (t.right != null) {            t.right.code = t.code + t.right.code;            code(t.right);        }    }    public static void print(TreeNode root) {        if (root != null) {            if (root.left == null && root.right == null) {                System.out.println(root.ch + " 编码：" + root.code);            }else {                print(root.left);                print(root.right);            }        }    }    public static void main(String[] args) {        TreeMap<Integer, Character> test = new TreeMap<>();        test.put(5, 'f');        test.put(9, 'e');        test.put(12, 'c');        test.put(13, 'b');        test.put(16, 'd');        test.put(45, 'a');        TreeNode root = huffman(test);        code(root);        print(root);    }}