Adding Huffman Coding Algorithm

aayushi2601 · abranhe · commit 7be7ef2152d8 · 2020-10-06T16:40:04.000-04:00
diff --git a/greedyalgorithms/HuffmanCoding.java b/greedyalgorithms/HuffmanCoding.java
@@ -0,0 +1,125 @@
+import java.util.PriorityQueue; 
+import java.util.Scanner; 
+import java.util.Comparator; 
+
+// Implementation of Hoffman Coding algoritms.
+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 adding 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, ""); 
+	} 
+} 
