java 根据哈夫曼编码求哈夫曼树

以下是Java中根据哈夫曼编码求哈夫曼树的示例代码：

import java.util.PriorityQueue;

public class HuffmanTree {
    public static Node buildTree(int[] charFreqs) {
        PriorityQueue<Node> trees = new PriorityQueue<Node>();
        for (int i = 0; i < charFreqs.length; i++) {
            if (charFreqs[i] > 0) {
                trees.offer(new LeafNode(charFreqs[i], (char) i));
            }
        }
        assert trees.size() > 0;
        while (trees.size() > 1) {
            Node a = trees.poll();
            Node b = trees.poll();
            trees.offer(new InternalNode(a, b));
        }
        return trees.poll();
    }

    public static class Node implements Comparable<Node> {
        public final int frequency;

        public Node(int freq) {
            frequency = freq;
        }

        public int compareTo(Node tree) {
            return frequency - tree.frequency;
        }
    }

    public static class InternalNode extends Node {
        public final Node left, right;

        public InternalNode(Node left, Node right) {
            super(left.frequency + right.frequency);
            this.left = left;
            this.right = right;
        }
    }

    public static class LeafNode extends Node {
        public final char value;

        public LeafNode(int freq, char val) {
            super(freq);
            value = val;
        }
    }
}

以上代码中，我们使用了优先队列来构建哈夫曼树。首先，我们将每个字符的出现频率作为权值，构建出叶子节点。然后，我们将所有叶子节点放入优先队列中，并不断取出队列中权值最小的两个节点，将它们合并成一个新的节点，并将新节点放回队列中。最终，队列中只剩下一个节点，即为哈夫曼树的根节点。