Huffman Code using Java

import java.util.Comparator;

import java.util.PriorityQueue;

import java.util.Scanner;

class Huffman {

// recursive function to print the 

// huffman-code through the tree traversal. 

// Here s is the huffman - code generated. 

public static void printCode(HuffmanNode root, String s) 

{ 



    // base case; if the left and right are null 

    // then its a leaf node and we print 

    // the code s generated by traversing the tree. 

    if (root.left == null && root.right == null

        && Character.isLetter(root.c)) { 



        // c is the character in the node 

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



        return; 

    } 



    // if we go to left then add "0" to the code. 

    // if we go to the right add"1" to the code. 



    // recursive calls for left and 

    // right sub-tree of the generated tree. 

    printCode(root.left, s + "0"); 

    printCode(root.right, s + "1"); 

} 



// main function 

public static void main(String[] args) 

{ 



    Scanner s = new Scanner(System.in); 



    // number of characters. 

    int n = 6; 

    char[] charArray = { 'a', 'b', 'c', 'd', 'e', 'f' }; 

    int[] charfreq = { 5, 9, 12, 13, 16, 45 }; 



    // creating a priority queue q. 

    // makes a min-priority queue(min-heap). 

    PriorityQueue<HuffmanNode> q 

        = new PriorityQueue<HuffmanNode>( 

            n, new MyComparator()); 



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



        // creating a Huffman node object 

        // and add it to the priority queue. 

        HuffmanNode hn = new HuffmanNode(); 



        hn.c = charArray[i]; 

        hn.data = charfreq[i]; 



        hn.left = null; 

        hn.right = null; 



        // add functions adds 

        // the huffman node to the queue. 

        q.add(hn); 

    } 



    // create a root node 

    HuffmanNode root = null; 



    // Here we will extract the two minimum value 

    // from the heap each time until 

    // its size reduces to 1, extract until 

    // all the nodes are extracted. 

    while (q.size() > 1) { 



        // first min extract. 

        HuffmanNode x = q.peek(); 

        q.poll(); 



        // second min extract. 

        HuffmanNode y = q.peek(); 

        q.poll(); 



        // new node f which is equal 

        HuffmanNode f = new HuffmanNode(); 



        // to the sum of the frequency of the two nodes 

        // assigning values to the f node. 

        f.data = x.data + y.data; 

        f.c = '-'; 



        // first extracted node as left child. 

        f.left = x; 



        // second extracted node as the right child. 

        f.right = y; 



        // marking the f node as the root node. 

        root = f; 



        // add this node to the priority-queue. 

        q.add(f); 

    } 



    // print the codes by traversing the tree 

    printCode(root, ""); 

} 

}

// node class is the basic structure
// of each node present in the Huffman - tree.

class HuffmanNode {

int data; 

char c; 



HuffmanNode left; 

HuffmanNode right; 

}

// comparator class helps to compare the node
// on the basis of one of its attribute.
// Here we will be compared
// on the basis of data values of the nodes.

class MyComparator implements Comparator<HuffmanNode> {

public int compare(HuffmanNode x, HuffmanNode y) 

{ 



    return x.data - y.data; 

} 

}