huffman.java

// Huffman Coding in Java

import java.util.PriorityQueue;
import java.util.Comparator;

class HuffmanNode {
  int item;
  char c;
  HuffmanNode left;
  HuffmanNode right;
}

// For comparing the nodes
class ImplementComparator implements Comparator<HuffmanNode> {
  public int compare(HuffmanNode x, HuffmanNode y) {
    return x.item - y.item;
  }
}

// IMplementing the huffman algorithm
public class Huffman {
  public static void printCode(HuffmanNode root, String s) {
    if (root.left == null && root.right == null && Character.isLetter(root.c)) {

      System.out.println(root.c + "   |  " + s);

      return;
    }
    printCode(root.left, s + "0");
    printCode(root.right, s + "1");
  }

  public static void main(String[] args) {

    int n = 4;
    char[] charArray = { 'A', 'B', 'C', 'D' };
    int[] charfreq = { 5, 1, 6, 3 };

    PriorityQueue<HuffmanNode> q = new PriorityQueue<HuffmanNode>(n, new ImplementComparator());

    for (int i = 0; i < n; i++) {
      HuffmanNode hn = new HuffmanNode();

      hn.c = charArray[i];
      hn.item = charfreq[i];

      hn.left = null;
      hn.right = null;

      q.add(hn);
    }

    HuffmanNode root = null;

    while (q.size() > 1) {

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

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

      HuffmanNode f = new HuffmanNode();

      f.item = x.item + y.item;
      f.c = '-';
      f.left = x;
      f.right = y;
      root = f;

      q.add(f);
    }
    System.out.println(" Char | Huffman code ");
    System.out.println("--------------------");
    printCode(root, "");
  }
}