day17-赫夫曼树

package com.summer.huffmantree;

import java.util.ArrayList;
import java.util.Collection;
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};
        Node huffmanTree = createHuffmanTree(arr);
        preOrder(huffmanTree);
    }

    public static Node createHuffmanTree(int arr[]){
        List<Node> nodes = new ArrayList<Node>();
        for (int i : arr) {
            nodes.add(new Node(i));
        }
        while (nodes.size()>1){
            Collections.sort(nodes);
            //取出数组中前两个节点，组成树
            Node left = nodes.get(0);
            Node right = nodes.get(1);
            Node parent = new Node(left.value+right.value,left,right);
            //删除取出的两个节点，将父节点加入
            nodes.remove(left);
            nodes.remove(right);
            nodes.add(parent);
        }
        return nodes.get(0);
    }

    public static void preOrder(Node node){
        if (node!=null){
            node.preOrder();
        }else {
            System.out.println("树为空");
        }
    }

}

//为了使Node支持排序，我们要实现Comparable接口
class Node implements Comparable<Node>{
    int value;
    Node left;
    Node right;

    public Node() {
    }

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

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

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

    @Override
    public int compareTo(Node o) {
        //从小到大排序
        return this.value - o.value;
    }

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