JavaAlgorithms/Others/Huffman.java

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Java
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2021-10-29 13:16:26 +08:00
import java.util.PriorityQueue;
import java.util.Scanner;
import java.util.Comparator;
// 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;
}
}
public 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 extarct.
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, "");
}
}