Java数据结构之哈夫曼树概述及实现

package DataStrcture.huffmantreedemo;

public class HTreenode implements Comparable<HTreeNode>{
    //
    public HTreeNode leftNode;
    public HTreeNode rightNode;
    public int weight;

    // 前序遍历
    public void preOrder(){

        System.out.println(this);

        if(this.leftNode != null) this.leftNode.preOrder();

        if(this.rightNode != null) this.rightNode.preOrder();
    }

    // 设置左右子节点
    public void setLeftNode(HTreeNode node){
        this.leftNode = node;
    }
    public void setRightNode(HTreeNode node){
        this.rightNode = node;
    }
    //构造方法和toString()
    public HTreeNode(int weight){
        this.weight = weight;
    }
    public String toString(){
        return "Node{weight: "+weight+"}";
    }
    //根据权值对结点进行排序
//    public int compareTo(Object obj){
//        return this.weight - ((HTreeNode)(obj)).weight;
//    }
    public int compareTo(HTreeNode node){
        return this.weight - node.weight;
    }
}

package DataStrcture.huffmantreedemo;

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

public class HuffmanTree{
    //哈夫曼树的实现:
    //1. 构建哈夫曼树的方法 buildHuffumanTree(int[] arr)
    //2. 对哈夫曼树进行遍历(二叉树遍历)
    public static void main(String[] args) {
        int[] arr = {13,7,8,3,29,6,1};
        HTreeNode hTreeNode = buildHuffmanTree(arr);
        preOrder(hTreeNode);
    }
    public static HTreeNode buildHuffmanTree(int[] arr){
        //
        ArrayList<HTreeNode> nodesList = new ArrayList<HTreeNode>();
        //1. 把存放权值的数组拿出来构建结点
        //2. 把这些节点存放到集合中
        for(int x : arr){
            nodesList.add(new HTreeNode(x));
        }
        while(nodesList.size() > 1){
            //3. 利用集合的排序方法,可以根据权值对结点进行排序
            Collections.sort(nodesList);
            // (当然了, 我们需要实现comparable接口中的copareTo方法), 在哪实现的? 在结点类中!
            //4. 不断的循环从集合中取出两个结点进行相加, 直到集合中只剩下一个结点才会终止循环
            HTreeNode leftNode = nodesList.get(0);
            HTreeNode rightNode = nodesList.get(1);

            HTreeNode parent = new HTreeNode(leftNode.weight + rightNode.weight);
            建立父节点和左右子节点的关系(千万不要忘了)
            //因为我们虽说是父节点和左右子节点, 还是要实实在在的于内存中体现出来的哈
            parent.setLeftNode(leftNode);
            parent.setRightNode(rightNode);
            //5.从结合中移除用过的左右子节点, 添加父节点进去
            nodesList.remove(leftNode);
            nodesList.remove(rightNode);
            nodesList.add(parent);
        }
        //6. 返回一个最终的唯一结点
        return nodesList.get(0);
    }
    //前序遍历哈夫曼树
    public static void preOrder(HTreeNode root){
        if(root != null){
            root.preOrder();
        }else{
            System.out.println("二叉树为空! ");
        }
    }
}