DesignAndAnalysisOfAlgorithms/Codes/Code_A2.java

import java.util.*;

public class Code_A2 {
    private static HuffmanNode root;
    private static Map<Character, String> huffmanCodes = new HashMap<>();
    private static Map<Character, Integer> freqMap = new HashMap<>();
    private static String inputText = "";

    static class HuffmanNode implements Comparable<HuffmanNode> {
        char ch;
        int freq;
        HuffmanNode left, right;

        HuffmanNode(char ch, int freq) {
            this.ch = ch;
            this.freq = freq;
        }

        public int compareTo(HuffmanNode other) {
            return this.freq - other.freq;
        }
    }

    private static void generateCodes(HuffmanNode node, String code) {
        if (node == null) return;
        if (node.left == null && node.right == null)
            huffmanCodes.put(node.ch, code);
        generateCodes(node.left, code + "0");
        generateCodes(node.right, code + "1");
    }

    private static void buildHuffmanTree() {
        PriorityQueue<HuffmanNode> pq = new PriorityQueue<>();
        for (Map.Entry<Character, Integer> e : freqMap.entrySet())
            pq.add(new HuffmanNode(e.getKey(), e.getValue()));

        while (pq.size() > 1) {
            HuffmanNode left = pq.poll();
            HuffmanNode right = pq.poll();
            HuffmanNode parent = new HuffmanNode('-', left.freq + right.freq);
            parent.left = left; parent.right = right;
            pq.add(parent);
        }
        root = pq.peek();
        huffmanCodes.clear();
        generateCodes(root, "");
    }

    private static void displayCodes() {
        if (huffmanCodes.isEmpty()) {
            System.out.println("No Huffman codes generated yet!");
            return;
        }
        System.out.println("\nCharacter\tFrequency\tHuffman Code");
        for (Map.Entry<Character, String> entry : huffmanCodes.entrySet())
            System.out.println(entry.getKey() + "\t\t" + freqMap.get(entry.getKey()) + "\t\t" + entry.getValue());
    }

    private static void encodeText() {
        if (huffmanCodes.isEmpty()) {
            System.out.println("Please build Huffman Tree first!");
            return;
        }
        StringBuilder encoded = new StringBuilder();
        for (char c : inputText.toCharArray())
            encoded.append(huffmanCodes.get(c));
        System.out.println("\nEncoded Text: " + encoded.toString());
    }

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        while (true) {
            System.out.println("\n=== Huffman Encoding Menu ===");
            System.out.println("1. Enter input string (auto frequency)");
            System.out.println("2. Enter characters with frequencies manually");
            System.out.println("3. Build Huffman Tree & display codes");
            System.out.println("4. Encode the text");
            System.out.println("5. Exit");
            System.out.print("Enter your choice: ");
            int choice = sc.nextInt();
            sc.nextLine();

            switch (choice) {
                case 1:
                    System.out.print("Enter the text: ");
                    inputText = sc.nextLine();
                    freqMap.clear();
                    for (char c : inputText.toCharArray())
                        freqMap.put(c, freqMap.getOrDefault(c, 0) + 1);
                    break;

                case 2:
                    freqMap.clear();
                    inputText = "";
                    System.out.print("Enter number of characters: ");
                    int n = sc.nextInt();
                    sc.nextLine();
                    for (int i = 0; i < n; i++) {
                        System.out.print("Character " + (i + 1) + ": ");
                        char c = sc.nextLine().charAt(0);
                        System.out.print("Frequency of " + c + ": ");
                        int f = sc.nextInt();
                        sc.nextLine();
                        freqMap.put(c, f);
                        inputText += String.valueOf(c).repeat(f);
                    }
                    break;

                case 3:
                    if (freqMap.isEmpty()) {
                        System.out.println("Please enter input first!");
                    } else {
                        buildHuffmanTree();
                        displayCodes();
                    }
                    break;

                case 4:
                    if (inputText.isEmpty())
                        System.out.println("Enter input text first!");
                    else
                        encodeText();
                    break;

                case 5:
                    System.out.println("Exiting program. Goodbye!");
                    sc.close();
                    return;

                default:
                    System.out.println("Invalid choice!");
            }
        }
    }
}