(哈夫曼樹)HuffmanTree的java實現

參考自：http://blog.csdn.net/jdhanhua/article/details/6621026

 

哈夫曼樹

哈夫曼樹（霍夫曼樹）又稱爲最優樹.

一、路徑和路徑長度
在一棵樹中，從一個結點往下能夠達到的孩子或孫子結點之間的通路，稱爲路徑。通路中分支的數目稱爲路徑長度。若規定根結點的層數爲1，則從根結點到第L層結點的路徑長

二、結點的權及帶權路徑長度
若將樹中結點賦給一個有着某種含義的數值，則這個數值稱爲該結點的權。結點的帶權路徑長度爲：從根結點到該結點之間的路徑長度與該結點的權的乘積。

三、樹的帶權路徑長度
樹的帶權路徑長度規定爲全部葉子結點的帶權路徑長度之和，記爲WPL。

 

代碼一（樹節點）：

/**
 * 樹節點
 * 
 * @author pang
 * 
 * @param <T>
 */
public class Node<T> implements Comparable<Node<T>> {
    private T data;
    private int weight;
    private Node<T> left;
    private Node<T> right;

    public Node(T data, int weight) {
        this.data = data;
        this.weight = weight;
    }

    @Override
    public String toString() {
        // TODO Auto-generated method stub
        return "data:" + this.data + ",weight:" + this.weight + ";   ";
    }

    @Override
    public int compareTo(Node<T> o) {
        // TODO Auto-generated method stub
        if (o.weight > this.weight) {
            return 1;
        } else if (o.weight < this.weight) {
            return -1;
        }
        return 0;
    }

    public T getData() {
        return data;
    }

    public void setData(T data) {
        this.data = data;
    }

    public int getWeight() {
        return weight;
    }

    public void setWeight(int weight) {
        this.weight = weight;
    }

    public Node<T> getLeft() {
        return left;
    }

    public void setLeft(Node<T> left) {
        this.left = left;
    }

    public Node<T> getRight() {
        return right;
    }

    public void setRight(Node<T> right) {
        this.right = right;
    }

}

 

代碼二（HuffmanTree）:

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

public class HuffmanTree<T> {

    public static <T> Node<T> createTree(List<Node<T>> nodes) {
        while (nodes.size() > 1) {
            Collections.sort(nodes);
            Node<T> left = nodes.get(nodes.size() - 1);
            Node<T> right = nodes.get(nodes.size() - 2);
            Node<T> parent = new Node<T>(null, left.getWeight()
                    + right.getWeight());
            parent.setLeft(left);
            parent.setRight(right);
            nodes.remove(left);
            nodes.remove(right);
            nodes.add(parent);
        }
        return nodes.get(0);
    }

    public static <T> List<Node<T>> breath(Node<T> root) {
        List<Node<T>> list = new ArrayList<Node<T>>();
        Queue<Node<T>> queue = new LinkedList<>();
        queue.add(root);
        while (!queue.isEmpty()) {
            Node<T> pNode = queue.poll();
            list.add(pNode);
            if (pNode.getLeft() != null) {
                queue.add(pNode.getLeft());
            }
            if (pNode.getRight() != null) {
                queue.add(pNode.getRight());
            }
        }
        return list;
    }

}

 

測試類：

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

public class HuffmanTreeTest {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        List<Node<String>> nodes = new ArrayList<Node<String>>();
        nodes.add(new Node<String>("b", 5));
        nodes.add(new Node<String>("a", 7));
        nodes.add(new Node<String>("d", 2));
        nodes.add(new Node<String>("c", 4));
        Node<String> root = HuffmanTree.createTree(nodes);
        System.out.println(HuffmanTree.breath(root));
    }

}