哈夫曼树生成代码Java

以下是Java中生成哈夫曼树的代码：

import java.util.PriorityQueue;

class HuffmanNode implements Comparable<HuffmanNode> {
    int frequency;
    char data;
    HuffmanNode left, right;

    public int compareTo(HuffmanNode node) {
        return frequency - node.frequency;
    }
}

public class HuffmanTree {
    public static void main(String[] args) {
        String message = "hello world";
        HuffmanNode root = buildTree(message);
        String encodedMessage = encode(root, message);
        System.out.println("Encoded message: " + encodedMessage);
        String decodedMessage = decode(root, encodedMessage);
        System.out.println("Decoded message: " + decodedMessage);
    }

    public static HuffmanNode buildTree(String message) {
        int[] frequency = new int[256];
        for (int i = 0; i < message.length(); i++) {
            frequency[message.charAt(i)]++;
        }

        PriorityQueue<HuffmanNode> pq = new PriorityQueue<>();
        for (char i = 0; i < 256; i++) {
            if (frequency[i] > 0) {
                HuffmanNode node = new HuffmanNode();
                node.data = i;
                node.frequency = frequency[i];
                node.left = null;
                node.right = null;
                pq.add(node);
            }
        }

        while (pq.size() > 1) {
            HuffmanNode left = pq.poll();
            HuffmanNode right = pq.poll();
            HuffmanNode parent = new HuffmanNode();
            parent.frequency = left.frequency + right.frequency;
            parent.data = '-';
            parent.left = left;
            parent.right = right;
            pq.add(parent);
        }

        return pq.poll();
    }

    public static String encode(HuffmanNode root, String message) {
        StringBuilder builder = new StringBuilder();
        for (int i = 0; i < message.length(); i++) {
            char c = message.charAt(i);
            HuffmanNode node = findNode(root, c);
            builder.append(node.data);
        }
        return builder.toString();
    }

    public static String decode(HuffmanNode root, String encodedMessage) {
        StringBuilder builder = new StringBuilder();
        HuffmanNode node = root;
        for (int i = 0; i < encodedMessage.length(); i++) {
            char c = encodedMessage.charAt(i);
            if (c == '0') {
                node = node.left;
            } else {
                node = node.right;
            }
            if (node.left == null && node.right == null) {
                builder.append(node.data);
                node = root;
            }
        }
        return builder.toString();
    }

    public static HuffmanNode findNode(HuffmanNode root, char c) {
        if (root == null) {
            return null;
        }
        if (root.data == c) {
            return root;
        }
        HuffmanNode left = findNode(root.left, c);
        if (left != null) {
            return left;
        }
        HuffmanNode right = findNode(root.right, c);
        if (right != null) {
            return right;
        }
        return null;
    }
}

这个代码中，`HuffmanNode`类表示哈夫曼树的节点，包含数据、频率以及左右子节点。`buildTree`方法根据输入的消息构建哈夫曼树，`encode`方法将输入的消息编码成哈夫曼编码，`decode`方法将哈夫曼编码解码成原始消息。`findNode`方法用来查找某个字符在哈夫曼树中对应的节点。