P1-P5: rewrite to match current syllabus

Signed-off-by: Amneesh Singh <natto@weirdnatto.in>

P1.java

@@ -1,8 +1,92 @@
-class P1 {
-  public static void main(String[] _args) {
-      int a = 44;
-      int b = 56;
+class Stack {
+    private int[] array;
+    private int top;
+    
+    public Stack(int capacity) {
+        array = new int[capacity];
+        top = -1;
+    }
+    
+    public void push(int item) {
+        if (top == array.length - 1) {
+            System.out.println("Stack Overflow");
+        } else {
+            array[++top] = item;
+            System.out.println("Pushed " + item + " to the stack");
+        }
+    }
+    
+    public int pop() {
+        if (top == -1) {
+            System.out.println("Stack Underflow");
+            return -1;
+        } else {
+            int item = array[top--];
+            System.out.println("Popped " + item + " from the stack");
+            return item;
+        }
+    }
+    
+    public boolean isEmpty() {
+        return top == -1;
+    }
+}
 
-      System.out.println(a + " + " + b + " = " + (a + b));
-  }
-}
+class Queue {
+    private int[] array;
+    private int front;
+    private int rear;
+    private int size;
+    
+    public Queue(int capacity) {
+        array = new int[capacity];
+        front = 0;
+        rear = -1;
+        size = 0;
+    }
+    
+    public void enqueue(int item) {
+        if (size == array.length) {
+            System.out.println("Queue is full");
+        } else {
+            rear = (rear + 1) % array.length;
+            array[rear] = item;
+            size++;
+            System.out.println("Enqueued " + item + " to the queue");
+        }
+    }
+    
+    public int dequeue() {
+        if (size == 0) {
+            System.out.println("Queue is empty");
+            return -1;
+        } else {
+            int item = array[front];
+            front = (front + 1) % array.length;
+            size--;
+            System.out.println("Dequeued " + item + " from the queue");
+            return item;
+        }
+    }
+    
+    public boolean isEmpty() {
+        return size == 0;
+    }
+}
+
+public class P1 {
+    public static void main(String[] args) {
+        Stack stack = new Stack(5);
+        stack.push(1);
+        stack.push(2);
+        stack.pop();
+        stack.pop();
+        stack.pop();
+        
+        Queue queue = new Queue(5);
+        queue.enqueue(1);
+        queue.enqueue(-4);
+        queue.dequeue();
+        queue.dequeue();
+    }
+}