Added links to all codes in readme.

Codes/Code-A5.py

@@ -0,0 +1,61 @@
+# Practical-A5 (N-Queen)
+
+"""
+THIS CODE HAS BEEN TESTED AND IS FULLY OPERATIONAL.
+
+Problem Statement: Design n-Queens matrix having first Queen placed. Use backtracking to place remaining Queens to generate the final n-queen‘s matrix.
+
+Code from DesignAndAnalysisOfAlgorithms (SPPU - Final Year - Computer Engineering - Content) repository on KSKA Git: https://git.kska.io/sppu-be-comp-content/DesignAndAnalysisOfAlgorithms/
+"""
+
+# BEGINNING OF CODE
+def placeQueens(i, cols, leftDiagonal, rightDiagonal, cur):
+    n = len(cols)
+
+    if i == n:
+        return True
+
+    for j in range(n):
+        if cols[j] or rightDiagonal[i + j] or leftDiagonal[i - j + n - 1]:
+            continue
+
+        cols[j] = 1 
+        rightDiagonal[i + j] = 1
+        leftDiagonal[i - j + n - 1] = 1
+        cur.append(j)
+
+        if placeQueens(i + 1, cols, leftDiagonal, rightDiagonal, cur):
+            return True
+
+        cur.pop()
+        cols[j] = 0
+        rightDiagonal[i + j] = 0
+        leftDiagonal[i - j + n - 1] = 0
+
+    return False
+
+def nQueen(n):
+    cols = [0] * n
+    leftDiagonal = [0] * (n * 2)
+    rightDiagonal = [0] * (n * 2)
+    cur = []
+    board = [['.' for _ in range(n)] for _ in range(n)]
+
+    if placeQueens(0, cols, leftDiagonal, rightDiagonal, cur):
+        for i in range(n):
+            board[i][cur[i]] = 'Q'
+        return board
+    else:
+        return None
+
+def printBoard(board):
+    if board:
+        for row in board:
+            print(" ".join(row))
+    else:
+        print("No solution exists.")
+
+n = int(input("Enter the number of queens:\t"))
+board = nQueen(n)
+printBoard(board)
+# END OF CODE

Codes/Code_A2.java

@@ -0,0 +1,135 @@
+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!");
+            }
+        }
+    }
+}

Codes/Code_A3.java

@@ -0,0 +1,83 @@
+import java.util.*;
+
+public class Code_A3 { // Main public class must match filename
+    static class Item {
+        int value, weight;
+        double ratio;
+
+        Item(int value, int weight) {
+            this.value = value;
+            this.weight = weight;
+            this.ratio = (double) value / weight;
+        }
+    }
+
+    public static void main(String[] args) {
+        Scanner sc = new Scanner(System.in);
+        List<Item> items = new ArrayList<>();
+        int choice;
+
+        while (true) {
+            System.out.println("\n=== Fractional Knapsack Menu ===");
+            System.out.println("1. Enter items");
+            System.out.println("2. Solve fractional knapsack");
+            System.out.println("3. Exit");
+            System.out.print("Enter your choice: ");
+            choice = sc.nextInt();
+
+            switch (choice) {
+                case 1:
+                    items.clear();
+                    System.out.print("Enter number of items: ");
+                    int n = sc.nextInt();
+                    for (int i = 0; i < n; i++) {
+                        System.out.print("Item " + (i + 1) + " value: ");
+                        int v = sc.nextInt();
+                        System.out.print("Item " + (i + 1) + " weight: ");
+                        int w = sc.nextInt();
+                        items.add(new Item(v, w));
+                    }
+                    break;
+
+                case 2:
+                    if (items.isEmpty()) {
+                        System.out.println("Please enter items first!");
+                        break;
+                    }
+                    System.out.print("Enter knapsack capacity: ");
+                    int capacity = sc.nextInt();
+
+                    // Sort by value-to-weight ratio
+                    items.sort((a, b) -> Double.compare(b.ratio, a.ratio));
+
+                    double totalValue = 0;
+                    int remaining = capacity;
+                    System.out.println("\nItems taken (value/weight fraction):");
+                    for (Item item : items) {
+                        if (remaining == 0) break;
+                        if (item.weight <= remaining) {
+                            System.out.println(item.value + "/" + item.weight + " -> Full");
+                            totalValue += item.value;
+                            remaining -= item.weight;
+                        } else {
+                            double fraction = (double) remaining / item.weight;
+                            System.out.println(item.value + "/" + item.weight + " -> " + (fraction * 100) + "%");
+                            totalValue += item.value * fraction;
+                            remaining = 0;
+                        }
+                    }
+
+                    System.out.printf("Maximum total value in knapsack: %.2f\n", totalValue);
+                    break;
+
+                case 3:
+                    System.out.println("Exiting program. Goodbye!");
+                    sc.close();
+                    return;
+
+                default:
+                    System.out.println("Invalid choice!");
+            }
+        }
+    }
+}

Codes/Code_A4.java

@@ -0,0 +1,171 @@
+// THIS CODE SHOWS DP-TABLE
+import java.util.*;
+
+public class Code_A4 {
+    public static void main(String[] args) {
+        Scanner sc = new Scanner(System.in);
+        int[] values = null;
+        int[] weights = null;
+        int n = 0;
+        int choice;
+
+        while (true) {
+            System.out.println("\n=== 0-1 Knapsack Menu ===");
+            System.out.println("1. Enter items (values & weights)");
+            System.out.println("2. Solve 0-1 Knapsack");
+            System.out.println("3. Exit");
+            System.out.print("Enter your choice: ");
+            choice = sc.nextInt();
+
+            switch (choice) {
+                case 1:
+                    System.out.print("Enter number of items: ");
+                    n = sc.nextInt();
+                    values = new int[n];
+                    weights = new int[n];
+
+                    for (int i = 0; i < n; i++) {
+                        System.out.print("Item " + (i + 1) + " value: ");
+                        values[i] = sc.nextInt();
+                        System.out.print("Item " + (i + 1) + " weight: ");
+                        weights[i] = sc.nextInt();
+                    }
+                    break;
+
+                case 2:
+                    if (values == null || weights == null || n == 0) {
+                        System.out.println("Please enter items first!");
+                        break;
+                    }
+
+                    System.out.print("Enter knapsack capacity: ");
+                    int capacity = sc.nextInt();
+
+                    int[][] dp = buildKnapsackDP(values, weights, n, capacity);
+                    System.out.println("\nDP Table:");
+                    printDPTable(dp, n, capacity);
+
+                    System.out.println("Maximum value that can be put in knapsack: " + dp[n][capacity]);
+                    break;
+
+                case 3:
+                    System.out.println("Exiting program. Goodbye!");
+                    sc.close();
+                    return;
+
+                default:
+                    System.out.println("Invalid choice!");
+            }
+        }
+    }
+
+    // Build DP table
+    private static int[][] buildKnapsackDP(int[] val, int[] wt, int n, int W) {
+        int[][] dp = new int[n + 1][W + 1];
+
+        for (int i = 0; i <= n; i++) {
+            for (int w = 0; w <= W; w++) {
+                if (i == 0 || w == 0)
+                    dp[i][w] = 0;
+                else if (wt[i - 1] <= w)
+                    dp[i][w] = Math.max(val[i - 1] + dp[i - 1][w - wt[i - 1]], dp[i - 1][w]);
+                else
+                    dp[i][w] = dp[i - 1][w];
+            }
+        }
+        return dp;
+    }
+
+    // Print DP table
+    private static void printDPTable(int[][] dp, int n, int W) {
+        System.out.print("   ");
+        for (int w = 0; w <= W; w++)
+            System.out.printf("%4d", w);
+        System.out.println();
+
+        for (int i = 0; i <= n; i++) {
+            System.out.printf("%2d ", i);
+            for (int w = 0; w <= W; w++)
+                System.out.printf("%4d", dp[i][w]);
+            System.out.println();
+        }
+    }
+}
+
+
+
+// THIS CODE DOESN'T SHOW DP-TABLE
+// import java.util.*;
+
+// public class ZeroOneKnapsack {
+//     public static void main(String[] args) {
+//         Scanner sc = new Scanner(System.in);
+//         int[] values = null;
+//         int[] weights = null;
+//         int n = 0;
+//         int choice;
+
+//         while (true) {
+//             System.out.println("\n=== 0-1 Knapsack Menu ===");
+//             System.out.println("1. Enter items (values & weights)");
+//             System.out.println("2. Solve 0-1 Knapsack");
+//             System.out.println("3. Exit");
+//             System.out.print("Enter your choice: ");
+//             choice = sc.nextInt();
+
+//             switch (choice) {
+//                 case 1:
+//                     System.out.print("Enter number of items: ");
+//                     n = sc.nextInt();
+//                     values = new int[n];
+//                     weights = new int[n];
+
+//                     for (int i = 0; i < n; i++) {
+//                         System.out.print("Item " + (i + 1) + " value: ");
+//                         values[i] = sc.nextInt();
+//                         System.out.print("Item " + (i + 1) + " weight: ");
+//                         weights[i] = sc.nextInt();
+//                     }
+//                     break;
+
+//                 case 2:
+//                     if (values == null || weights == null || n == 0) {
+//                         System.out.println("Please enter items first!");
+//                         break;
+//                     }
+
+//                     System.out.print("Enter knapsack capacity: ");
+//                     int capacity = sc.nextInt();
+
+//                     int maxValue = knapsackDP(values, weights, n, capacity);
+//                     System.out.println("Maximum value that can be put in knapsack: " + maxValue);
+//                     break;
+
+//                 case 3:
+//                     System.out.println("Exiting program. Goodbye!");
+//                     sc.close();
+//                     return;
+
+//                 default:
+//                     System.out.println("Invalid choice!");
+//             }
+//         }
+//     }
+
+//     // DP solution for 0-1 Knapsack
+//     private static int knapsackDP(int[] val, int[] wt, int n, int W) {
+//         int[][] dp = new int[n + 1][W + 1];
+
+//         for (int i = 0; i <= n; i++) {
+//             for (int w = 0; w <= W; w++) {
+//                 if (i == 0 || w == 0)
+//                     dp[i][w] = 0;
+//                 else if (wt[i - 1] <= w)
+//                     dp[i][w] = Math.max(val[i - 1] + dp[i - 1][w - wt[i - 1]], dp[i - 1][w]);
+//                 else
+//                     dp[i][w] = dp[i - 1][w];
+//             }
+//         }
+//         return dp[n][W];
+//     }
+// }

README.md

@@ -18,6 +18,10 @@ This repository contains valuable resources for the Design and Analysis of Algor
 ### Codes
 
 1. [Code-A1 - Fibonacci Series](Codes/Code-A1.py)
+2. [Code-A2 - Huffman Coding](Codes/Code_A2.java)
+3. [Code-A3 - Fractical Knapsack](Codes/Code_A3.java)
+4. [Code-A4 - 0/1 Knapsack](Codes/Code_A4.java)
+5. [Code-A5 - N-Queen Problem](Codes/Code-A5.py)
 
 ### Practical