HuffmanCoding

用Java实现的huffman编码树(仅对26个字符）。
1.使用的是26字符的频率作为各字符的权值
2.使用到最小堆，用java.util.PriorityQueue类实现。
3.各huffman node需要实现java.lang.Comparable接口

/**
* HuffmanTreeNode.java
*/
package Huffman;
/**
* @function :
* @author     :hjh
* @company    :fdu
* @date         :2009-10-23
*/
public class HuffmanTreeNode implements Comparable<HuffmanTreeNode>{
   private char ch; //if node is leaf, this value is valid  
   private boolean leaf;
   private float weight; //frequency
   private HuffmanTreeNode leftChild;
   private HuffmanTreeNode rightChild;
   private String huffmanCode;
  
   /**
    * @param c
    * @param weight
    */
   public HuffmanTreeNode( char c, float weight) {
     // constructor for leaf node
     this.ch = c;
     this.weight = weight;
     this.leaf = true;
     this.leftChild = null;
     this.rightChild = null;
     this.huffmanCode = "";
  }
   public HuffmanTreeNode( float weight,HuffmanTreeNode leftChild,HuffmanTreeNode rightChild) {
     // constructor for none-leaf node
     this.ch = '#';
     this.weight = weight;
     this.leaf = false;
     this.leftChild = leftChild;
     this.rightChild = rightChild;
     this.huffmanCode = "";
  }
   public char getCh() {
     return ch;
  }
   public void setCh( char ch) {
     this.ch = ch;
  }
   public boolean isLeaf() {
     return leaf;
  }
   public void setLeaf( boolean leaf) {
     this.leaf = leaf;
  }
   public float getWeight() {
     return weight;
  }
   public void setWeight( float weight) {
     this.weight = weight;
  }
   public HuffmanTreeNode getLeftChild() {
     return leftChild;
  }
   public void setLeftChild(HuffmanTreeNode leftChild) {
     this.leftChild = leftChild;
  }
   public HuffmanTreeNode getRightChild() {
     return rightChild;
  }
   public void setRightChild(HuffmanTreeNode rightChild) {
     this.rightChild = rightChild;
  }
   public String getHuffmanCode() {
     return huffmanCode;
  }
   public void setHuffmanCode(String huffmanCode) {
     this.huffmanCode = huffmanCode;
  }

   /* (non-Javadoc)
    * @see java.lang.Comparable#compareTo(java.lang.Object)
    */
  @Override
   public int compareTo(HuffmanTreeNode o) {
     return weight==o.weight?0:(weight<o.weight?-1:1);
  }
   public String toString(){    
     return weight+ "@"+huffmanCode+ "@"+ch;
  }  
}

主函数

/**
* HuffmanCoding.java
*/
package Huffman;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.util.PriorityQueue;

/**
* @function :
* @author     :hjh
* @company    :fdu
* @date         :2009-10-23
*/
public class HuffmanCoding {
  
   //the symbol table of 26 characters
   static HuffmanTreeNode[] nodes= new HuffmanTreeNode[26];  
  
   static void initial() {

    BufferedReader br = null;
     try {
      br = new BufferedReader( new FileReader( "bin/resource/abcfreqs.txt"));
    } catch (FileNotFoundException e) {
       // TODO Auto-generated catch block
      e.printStackTrace();
    }
    String line = null;
     try {
      line = br.readLine();
    } catch (IOException e) {
      e.printStackTrace();
    }
     float[] freqs = new float[26];
     char[] chars= new char[26];
    String[] strs = line.split( " ");
     for ( int i = 0,j=0; i<chars.length && j < strs.length; i++,j+=2) {
      chars[i]= strs[j].charAt(0);
      freqs[i] = Float.valueOf(strs[j+1]) * 0.01f;      
      nodes[i]= new HuffmanTreeNode(chars[i],freqs[i]);
    }    
  }
  
   public static void main(String args[]){
    initial();
     //create a minimum heap
    PriorityQueue<HuffmanTreeNode> minHeap = new PriorityQueue<HuffmanTreeNode>();
     for (HuffmanTreeNode node : nodes) {
      minHeap.offer(node);
    }
    HuffmanTreeNode root=genHuffmanTree(minHeap);
    dfsEncoding(root);        
    enCoding();
  }
  
   private static void enCoding() {  
     try {
      BufferedReader br = new BufferedReader( new FileReader( "bin/resource/input.txt"));
      BufferedWriter bw = new BufferedWriter( new FileWriter( "bin/resource/output.txt", false));

      String line;
       while ((line = br.readLine()) != null) {
        StringBuffer buf = new StringBuffer();
         for ( int i = 0; i < line.length(); i++) {
           char c = line.charAt(i);
          String huffcode=nodes[c-'A'].getHuffmanCode();
          buf.append(huffcode);
        }        
        bw.write(buf.toString());
        bw.newLine();
      }
      bw.flush();
      bw.close();
      br.close();
    } catch (IOException e) {
      e.printStackTrace();
    }
  }

   private static void dfsEncoding(HuffmanTreeNode root) {
     if(root== null)
       return;
     if(root.getLeftChild()== null && root.getRightChild()== null){
       //System.out.println(root);
       return;
    }
     if(root.getLeftChild()!= null){
      root.getLeftChild().setHuffmanCode(root.getHuffmanCode()+ "0");
      dfsEncoding(root.getLeftChild());
    }
     if(root.getRightChild()!= null){
      root.getRightChild().setHuffmanCode(root.getHuffmanCode()+ "1");
      dfsEncoding(root.getRightChild());
    }
    
  }

   /**
    *
    * @param minHeap
    * @return
    */
   private static HuffmanTreeNode genHuffmanTree(PriorityQueue<HuffmanTreeNode> minHeap) {
     while (!minHeap.isEmpty()) {
      HuffmanTreeNode n1 = minHeap.poll();
       if(minHeap.isEmpty())
         return n1;
      HuffmanTreeNode n2 = minHeap.poll();
       float weight=n1.getWeight()+n2.getWeight();
      HuffmanTreeNode s = new HuffmanTreeNode(weight,n1,n2);
      minHeap.offer(s);
    }
     return null;
  }
}