赫夫曼树

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};
        preOrder(createHuffmanTree(arr));
    }

    public static void preOrder(Node root){
        if (root!=null){
            root.preOrder();
        }
    }

    public static Node createHuffmanTree(int[] arr) {
        List<Node> nodes = new ArrayList<Node>();
        for (int value : arr) {
            nodes.add(new Node(value));
        }

        while (nodes.size() > 1) {
            //排序
            Collections.sort(nodes);
            //取最小两个值
            Node leftNode = nodes.get(0);
            Node rightNode = nodes.get(1);
            //创建最小树
            Node parent = new Node(leftNode.value + rightNode.value);
            parent.left = leftNode;
            parent.right = rightNode;
            //移除已经添加到树的节点
            nodes.remove(leftNode);
            nodes.remove(rightNode);
            //添加新树的最小节点
            nodes.add(parent);
        }
        return nodes.get(0);
    }
}

class Node implements Comparable<Node> {
    int value;
    Node left;
    Node right;

    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;
    }
}