javascript-algorithms/Huffman Coding/huffman.js

// node class is the basic structure
// of each node present in the Huffman - tree.
class HuffmanNode
{
	constructor()
	{
		this.data = 0;
		this.c = '';
		this.left = this.right = null;
	}
}

// recursive function to print the
	// huffman-code through the tree traversal.
	// Here s is the huffman - code generated.
	function printCode(root,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
			&& (root.c).toLowerCase() != (root.c).toUpperCase()) {

			// c is the character in the node
			document.write(root.c + ":" + s+"<br>");

			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
// number of characters.
		let n = 6;
		let charArray = [ 'a', 'b', 'c', 'd', 'e', 'f' ];
		let charfreq = [ 5, 9, 12, 13, 16, 45 ];

		// creating a priority queue q.
		// makes a min-priority queue(min-heap).
		let q = [];

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

			// creating a Huffman node object
			// and add it to the priority queue.
			let 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.push(hn);
		}

		// create a root node
		let root = null;
		q.sort(function(a,b){return a.data-b.data;});
		
		// 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.length > 1) {

			// first min extract.
			let x = q[0];
			q.shift();

			// second min extract.
			let y = q[0];
			q.shift();

			// new node f which is equal
			let 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.push(f);
			q.sort(function(a,b){return a.data-b.data;});
		}

		// print the codes by traversing the tree
		printCode(root, "");

// This code is contributed by avanitrachhadiya2155