11、创建Huffman树，生成Huffman编码

package ren.laughing.datastructure.baseImpl;

import ren.laughing.datastructure.base.List;

/**
 * 创建Huffman树
 * 生成Huffman编码
 * @author Laughing_Lz
 * @time 2016年4月14日
 */
public class HuffmanTree {
    /**
     * 创建Huffman树
     * @param nodes
     * @return
     */
    public HuffmanTreeNode buildHuffmanTree(HuffmanTreeNode[] nodes){
        int n = nodes.length;
        if(n < 2){
            return nodes[0];
        }
        List list = new ArrayList();
        for(int i = 0;i<nodes.length;i++){
            insertList(list,nodes[i]);//按照nodes的weight从大到小顺序存入list中
        }
        for(int i = 1;i<n;i++){//选择 weight 最小的两棵树合并，循环 n-1 次
            HuffmanTreeNode minNode1 = (HuffmanTreeNode) list.remove(list.getSize()-1);
            HuffmanTreeNode minNode2 = (HuffmanTreeNode) list.remove(list.getSize()-1);
            HuffmanTreeNode newNode = new HuffmanTreeNode(minNode1.getWeight()+minNode2.getWeight(), "root");
            newNode.setLChild(minNode1);
            newNode.setRChild(minNode2);
            insertList(list, newNode);//重新插入list中
        }
        return (HuffmanTreeNode) list.get(0);
    }
    /**
     * 将huffmanTreeNode按weight从大到小存入list中
     * @param list
     * @param huffmanTreeNode
     */
    private void insertList(List list, HuffmanTreeNode node) {
        for(int i = 0;i<list.getSize();i++){
            if(node.getWeight()>((HuffmanTreeNode)list.get(i)).getWeight()){//★
                list.insert(i, node);
                return;
            }
        }
        list.insert(list.getSize(), node);//若node的weight最小，放在list最后
        return;
    }
    /**
     * 生成Huffman编码
     * @param root
     */
    public void generateHuffmanCode(HuffmanTreeNode root){
        if(root == null){
            return;
        }
        if(root.hasParent()){
            if(root.isLChild()){
                root.setCoding(root.getParent().getCoding()+"0");
            }
            if(root.isRChild()){
                root.setCoding(root.getParent().getCoding()+"1");
            }
        }
        generateHuffmanCode(root.getLChild());
        generateHuffmanCode(root.getRChild());
    }
    public static void main(String[] args) {
        HuffmanTreeNode[] nodes = creatHuffmanNodes();
        HuffmanTree huffmanTree = new HuffmanTree();
        HuffmanTreeNode root = huffmanTree.buildHuffmanTree(nodes);
        System.out.println("构建的Huffman树根结点是"+root.getData()+",高度为："+root.getHeight()+",权值为："+root.getWeight());
        huffmanTree.generateHuffmanCode(root);
        System.out.println(root.getRChild().getRChild().getLChild().getCoding());//★Huffman编码针对叶子结点，root结点无编码
    }
    /**
     * 创建HuffmanNode结点组合
     * @return
     */
    public static HuffmanTreeNode[] creatHuffmanNodes(){
        HuffmanTreeNode[] nodes = new HuffmanTreeNode[7];
        HuffmanTreeNode node1 = new HuffmanTreeNode(1, 'A');
        HuffmanTreeNode node2 = new HuffmanTreeNode(2, 'B');
        HuffmanTreeNode node3 = new HuffmanTreeNode(3, 'C');
        HuffmanTreeNode node4 = new HuffmanTreeNode(4, 'D');
        HuffmanTreeNode node5 = new HuffmanTreeNode(5, 'E');
        HuffmanTreeNode node6 = new HuffmanTreeNode(6, 'F');
        HuffmanTreeNode node7 = new HuffmanTreeNode(7, 'G');
        nodes[0] = node2;
        nodes[1] = node5;
        nodes[2] = node1;
        nodes[3] = node3;
        nodes[4] = node4;
        nodes[5] = node7;
        nodes[6] = node6;
        return nodes;
    }
}