Question

Read through "The Huffman Code" on page 415 of the book. Write a program to implement Huffman coding and decoding. It should do the following: Accept a text message, possibly of more than one line. Create a Huffman tree for this message. Create a code table. Encode the message into binary. Decode the message from binary back to text. in JAVA

Answer 1

solution:

given data:

JAVA

import java.util.HashMap;
import java.util.Map;
import java.util.PriorityQueue;
import java.util.Set;
import java.util.Map.*;

class HuffmanNode implements Comparable<HuffmanNode> {
int frequency;
char data;
HuffmanNode left, right;

public int compareTo(HuffmanNode node) {
return frequency - node.frequency;
}
}

public class Solution
{
private static Map<Character, String> charPrefixHashMap = new HashMap<>();
   static HuffmanNode root;

   public static void main(String[] args) {

       String test = "This is a new message";
       System.out.println("Original Text = "+test);
       String s = encode(test);
       decode(s);

   }

   private static HuffmanNode buildTree(Map<Character, Integer> freq) {

       PriorityQueue<HuffmanNode> priorityQueue = new PriorityQueue<>();
       Set<Character> keySet = freq.keySet();
       for (Character c : keySet) {

           HuffmanNode huffmanNode = new HuffmanNode();
           huffmanNode.data = c;
           huffmanNode.frequency = freq.get(c);
           huffmanNode.left = null;
           huffmanNode.right = null;
           priorityQueue.offer(huffmanNode);
       }
       assert priorityQueue.size() > 0;

       while (priorityQueue.size() > 1) {

           HuffmanNode x = priorityQueue.peek();
           priorityQueue.poll();

           HuffmanNode y = priorityQueue.peek();
           priorityQueue.poll();

           HuffmanNode sum = new HuffmanNode();

           sum.frequency = x.frequency + y.frequency;
           sum.data = '-';

           sum.left = x;

           sum.right = y;
           root = sum;

           priorityQueue.offer(sum);
       }

       return priorityQueue.poll();
   }

   private static void setPrefixCodes(HuffmanNode node, StringBuilder prefix) {

       if (node != null) {
           if (node.left == null && node.right == null) {
               charPrefixHashMap.put(node.data, prefix.toString());

           } else {
               prefix.append('0');
               setPrefixCodes(node.left, prefix);
               prefix.deleteCharAt(prefix.length() - 1);

               prefix.append('1');
               setPrefixCodes(node.right, prefix);
               prefix.deleteCharAt(prefix.length() - 1);
           }
       }

   }

   private static String encode(String test) {
       Map<Character, Integer> freq = new HashMap<>();
       for (int i = 0; i < test.length(); i++) {
           if (!freq.containsKey(test.charAt(i))) {
               freq.put(test.charAt(i), 0);
           }
           freq.put(test.charAt(i), freq.get(test.charAt(i)) + 1);
       }

//        System.out.println("Character Frequency Map = " + freq);
System.out.println("Code Table");
freq.entrySet().forEach(entry->{
System.out.println(entry.getKey() + " ------------------- " + entry.getValue());
});
       root = buildTree(freq);

       setPrefixCodes(root, new StringBuilder());
       System.out.println("Character Prefix Map = " + charPrefixHashMap);
       StringBuilder s = new StringBuilder();

       for (int i = 0; i < test.length(); i++) {
           char c = test.charAt(i);
           s.append(charPrefixHashMap.get(c));
       }

       return s.toString();
   }

   private static void decode(String s) {

       StringBuilder stringBuilder = new StringBuilder();

       HuffmanNode temp = root;

       System.out.println("Encoded: " + s);

       for (int i = 0; i < s.length(); i++) {
           int j = Integer.parseInt(String.valueOf(s.charAt(i)));

           if (j == 0) {
               temp = temp.left;
               if (temp.left == null && temp.right == null) {
                   stringBuilder.append(temp.data);
                   temp = root;
               }
           }
           if (j == 1) {
               temp = temp.right;
               if (temp.left == null && temp.right == null) {
                   stringBuilder.append(temp.data);
                   temp = root;
               }
           }
       }

       System.out.println("Decoded string is : " + stringBuilder.toString());

   }
}

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