哈夫曼树（Java）

package DataStructures.huffmantree;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class HuffmanTree {
    public static void main(String[] args) {
        int[] arr = {13,7,8,3,29,6,1};
//        createHuffmanTree(arr);

        preOrder(createHuffmanTree(arr));

    }

    //前序遍历
    public static void preOrder(Node node){
        if (node != null){
            node.preOrder();
        } else {
            System.out.println("该哈夫曼树为空！");
        }
    }

    //创建哈夫曼树
    public static Node createHuffmanTree(int[] arr){
        //1.遍历数组
        //2.将每个数组元素构建为Node
        //3.将Node放入到ArrayList中
        List nodeList = new ArrayList();
        for(int value: arr){
            nodeList.add(new Node(value));
        }

        while (nodeList.size() > 1) {
            //排序
            Collections.sort(nodeList);
//            System.out.println(nodeList);

            
            Node leftNode = nodeList.get(0);
            Node rightNode = nodeList.get(1);
            //构建新二叉树
            Node parent = new Node(leftNode.value + rightNode.value);
            parent.left = leftNode;
            parent.right = rightNode;

            //从ArrayList中删除0，1
            nodeList.remove(leftNode);
            nodeList.remove(rightNode);
            //将parent加入到nodeList
            nodeList.add(parent);
        }
        return nodeList.get(0);
    }
}

//创建节点类
class Node implements Comparable{
    int value;
    Node left;
    Node right;

    //前序遍历
    public void preOrder(){
        System.out.println(this);
        if(this.left != null){
            this.left.preOrder();
        }
        if (this.right != null){
            this.right.preOrder();
        }
    }

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

    @Override
    public String toString() {
        return "Node{" +
                "value=" + value +
                '}';
    }

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