Added Circular Queue data structure

Author: sonudodwariya

src/main/java/com/thealgorithms/datastructures/queues/DequeUsingArray.java

@@ -0,0 +1,159 @@
+package com.thealgorithms.datastructures.queues;
+
+/**
+ * Implementation of a Double Ended Queue (Deque) using Array
+ * A deque allows insertion and deletion from both front and rear ends.
+ * Author: Sonu Dodwariya (Hacktoberfest 2025)
+ */
+
+public class DequeUsingArray {
+
+    private int[] arr;
+    private int front;
+    private int rear;
+    private int size;
+
+    // Constructor
+    public DequeUsingArray(int size) {
+        arr = new int[size];
+        front = -1;
+        rear = 0;
+        this.size = size;
+    }
+
+    // Check if deque is full
+    public boolean isFull() {
+        return (front == 0 && rear == size - 1) || (front == rear + 1);
+    }
+
+    // Check if deque is empty
+    public boolean isEmpty() {
+        return (front == -1);
+    }
+
+    // Insert element at front
+    public void insertFront(int key) {
+        if (isFull()) {
+            System.out.println("Deque is full!");
+            return;
+        }
+
+        // First element
+        if (front == -1) {
+            front = 0;
+            rear = 0;
+        } else if (front == 0)
+            front = size - 1;
+        else
+            front = front - 1;
+
+        arr[front] = key;
+    }
+
+    // Insert element at rear
+    public void insertRear(int key) {
+        if (isFull()) {
+            System.out.println("Deque is full!");
+            return;
+        }
+
+        // First element
+        if (front == -1) {
+            front = 0;
+            rear = 0;
+        } else if (rear == size - 1)
+            rear = 0;
+        else
+            rear = rear + 1;
+
+        arr[rear] = key;
+    }
+
+    // Delete element at front
+    public void deleteFront() {
+        if (isEmpty()) {
+            System.out.println("Deque is empty!");
+            return;
+        }
+
+        // Single element
+        if (front == rear) {
+            front = -1;
+            rear = -1;
+        } else if (front == size - 1)
+            front = 0;
+        else
+            front = front + 1;
+    }
+
+    // Delete element at rear
+    public void deleteRear() {
+        if (isEmpty()) {
+            System.out.println("Deque is empty!");
+            return;
+        }
+
+        // Single element
+        if (front == rear) {
+            front = -1;
+            rear = -1;
+        } else if (rear == 0)
+            rear = size - 1;
+        else
+            rear = rear - 1;
+    }
+
+    // Get front element
+    public int getFront() {
+        if (isEmpty()) {
+            System.out.println("Deque is empty!");
+            return -1;
+        }
+        return arr[front];
+    }
+
+    // Get rear element
+    public int getRear() {
+        if (isEmpty() || rear < 0) {
+            System.out.println("Deque is empty!");
+            return -1;
+        }
+        return arr[rear];
+    }
+
+    // Display all elements
+    public void display() {
+        if (isEmpty()) {
+            System.out.println("Deque is empty!");
+            return;
+        }
+
+        System.out.print("Deque elements: ");
+        int i = front;
+        while (true) {
+            System.out.print(arr[i] + " ");
+            if (i == rear)
+                break;
+            i = (i + 1) % size;
+        }
+        System.out.println();
+    }
+
+    // Main method for testing
+    public static void main(String[] args) {
+        DequeUsingArray dq = new DequeUsingArray(5);
+
+        dq.insertRear(10);
+        dq.insertRear(20);
+        dq.insertFront(5);
+        dq.insertFront(2);
+        dq.display();
+
+        System.out.println("Front element: " + dq.getFront());
+        System.out.println("Rear element: " + dq.getRear());
+
+        dq.deleteFront();
+        dq.deleteRear();
+        dq.display();
+    }
+}