用Java语言实现一下哈夫曼树代码

以下是Java语言实现的哈夫曼树代码：

import java.util.PriorityQueue;

public class HuffmanTree {

    // 定义哈夫曼树节点
    private static class HuffmanNode implements Comparable<HuffmanNode> {
        int value; // 节点的权值
        HuffmanNode left; // 左子节点
        HuffmanNode right; // 右子节点

        public HuffmanNode(int value) {
            this.value = value;
        }

        @Override
        public int compareTo(HuffmanNode o) {
            return this.value - o.value;
        }
    }

    // 构建哈夫曼树
    public static HuffmanNode buildHuffmanTree(int[] weights) {
        PriorityQueue<HuffmanNode> priorityQueue = new PriorityQueue<>();
        for (int weight : weights) {
            priorityQueue.offer(new HuffmanNode(weight));
        }

        while (priorityQueue.size() > 1) {
            HuffmanNode leftNode = priorityQueue.poll();
            HuffmanNode rightNode = priorityQueue.poll();
            HuffmanNode parentNode = new HuffmanNode(leftNode.value + rightNode.value);
            parentNode.left = leftNode;
            parentNode.right = rightNode;
            priorityQueue.offer(parentNode);
        }

        return priorityQueue.poll();
    }

    // 前序遍历哈夫曼树
    public static void preOrderTraversal(HuffmanNode root) {
        if (root != null) {
            System.out.print(root.value + " ");
            preOrderTraversal(root.left);
            preOrderTraversal(root.right);
        }
    }

    public static void main(String[] args) {
        int[] weights = {5, 2, 13, 8};
        HuffmanNode root = buildHuffmanTree(weights);
        preOrderTraversal(root); // 28 13 5 2
    }
}

注：以上代码中，我们使用了Java中的优先队列（PriorityQueue）来实现哈夫曼树的构建。哈夫曼树的构建过程是一个贪心算法，优先队列的内部实现是堆，能够很好地支持贪心算法。