(哈夫曼树)HuffmanTree的java实现

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

哈夫曼树

哈夫曼树（霍夫曼树）又称为最优树.

1、路径和路径长度
在一棵树中，从一个结点往下可以达到的孩子或孙子结点之间的通路，称为路径。通路中分支的数目称为路径长度。若规定根结点的层数为1，则从根结点到第L层结点的路径长

2、结点的权及带权路径长度
若将树中结点赋给一个有着某种含义的数值，则这个数值称为该结点的权。结点的带权路径长度为：从根结点到该结点之间的路径长度与该结点的权的乘积。

3、树的带权路径长度
树的带权路径长度规定为所有叶子结点的带权路径长度之和，记为WPL。

代码一（树节点）：

/**
* 树节点
*
* @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;
}

}

代码二（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;
}

}

测试类：

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));
}

}