Circular Queue in JAVA (jainaman224#2471)

* Added Circular_Queue.java

* Added Circular_Queue.java

Co-authored-by: pratilipi <pratilipiaich@gmail.com>

Circular_Queue/Circular_Queue.java

@@ -0,0 +1,248 @@
+/* Circular Queue works by the process of circular increment
+i.e. when we try to increment any variable and we reach the end of queue,
+we start from the beginning of queue by modulo division with the queue size.*/
+
+import java.util.Scanner;
+
+public class Circular_Queue {
+    int front, rear, size;
+    int[] arr;
+
+    public Circular_Queue(int s) {
+        size = s;
+        arr = new int[s];
+        front = rear = -1;
+    }
+
+    public static void main(String[] args) {
+        int choice, value, s;
+        Scanner in = new Scanner(System.in);
+
+        System.out.println("Enter the size of queue:");
+        s = in.nextInt();
+        Circular_Queue q = new Circular_Queue(s);
+        do {
+            System.out.println("\n1. Insert");
+            System.out.println("2. Delete");
+            System.out.println("3. Display");
+            System.out.println("4. Exit");
+            System.out.println("Enter choice: ");
+            choice = in.nextInt();
+            switch (choice) {
+                case 1:
+                    System.out.println("\nEnter the value: ");
+                    value = in.nextInt();
+                    q.enQueue(value);
+                    break;
+                case 2:
+                    value = q.deQueue();
+                    if(value == -1) {
+                        System.out.println("\nUNDERFLOW! Queue is Empty.");
+                        break;
+                    }
+                    System.out.println("\n" + value + " Deleted from queue.");
+                    break;
+                case 3:
+                    q.display();
+                    break;
+                case 4:
+                    System.exit(0);
+                default:
+                    System.out.println("Invalid choice.");
+
+            }
+        } while (choice != 4);
+
+    }
+
+    /*
+Insertion:
+1) Check whether queue is Full by (front == 0 && rear == size - 1) || (rear == (front - 1) % (size - 1)).
+2) If it is full then display Queue is full. If queue is not full then, check
+    if (front == -1) then set front = rear = 0 and insert the first element.
+3) If (rear == SIZE – 1 && front != 0) if it is true then set rear = 0 and insert element.
+4) Otherwise increment rear by 1 and insert an element.
+*/
+// Inserting the value in the queue
+    public void enQueue(int value) {
+        if ((front == 0 && rear == size - 1) ||
+                (rear == (front - 1) % (size - 1))) {
+            System.out.println("\nOVERFLOW! Queue is Full.");
+            return;
+        } else if (front == -1) /* Insert First Element */ {
+            front = rear = 0;
+            arr[rear] = value;
+        } else if (rear == size - 1 && front != 0) {
+            rear = 0;
+            arr[rear] = value;
+        } else {
+            rear++;
+            arr[rear] = value;
+        }
+    }
+
+    /*
+Deletion:
+1) Check whether queue is Empty with (front==-1).
+2) If it is empty then display Queue is empty.
+3) If queue is not empty then remove the element and Check if (front==rear)
+   if it is true then set front = rear= -1 else set front = (front + 1) % size and return the element.
+*/
+// Deleting from queue
+    public int deQueue() {
+        if (front == -1) {
+            return -1;
+
+        }
+        int element = arr[front];
+        arr[front] = -1;
+        if (front == rear) {
+            front = -1;
+            rear = -1;
+        }
+        else {
+            if (front == size - 1)
+                front = 0;
+            else
+                front = front + 1;
+        }
+        return element;
+    }
+
+    // Displaying the queue
+    public void display() {
+        if (front == -1) {
+            System.out.println("UNDERFLOW! Queue is Empty.");
+            return;
+        }
+        System.out.println("\nElements in Circular Queue are: ");
+        if (rear >= front) {
+            for (int i = front; i <= rear; i++)
+                System.out.print(arr[i] + "\t");
+        } else {
+            for (int i = front; i < size; i++)
+                System.out.println(arr[i] + "\t");
+
+            for (int i = 0; i <= rear; i++)
+                System.out.println(arr[i] + "\t");
+        }
+    }
+
+}
+/*
+Enter the size of queue:
+4
+
+1. Insert
+2. Delete
+3. Display
+4. Exit
+Enter choice:
+1
+
+Enter the value:
+10
+
+1. Insert
+2. Delete
+3. Display
+4. Exit
+Enter choice:
+1
+
+Enter the value:
+20
+
+1. Insert
+2. Delete
+3. Display
+4. Exit
+Enter choice:
+1
+
+Enter the value:
+30
+
+1. Insert
+2. Delete
+3. Display
+4. Exit
+Enter choice:
+1
+
+Enter the value:
+40
+
+1. Insert
+2. Delete
+3. Display
+4. Exit
+Enter choice:
+1
+
+Enter the value:
+50
+
+OVERFLOW! Queue is Full.
+
+1. Insert
+2. Delete
+3. Display
+4. Exit
+Enter choice:
+3
+
+Elements in Circular Queue are:
+10	20	30	40
+1. Insert
+2. Delete
+3. Display
+4. Exit
+Enter choice:
+2
+
+10 Deleted from queue.
+
+1. Insert
+2. Delete
+3. Display
+4. Exit
+Enter choice:
+2
+
+20 Deleted from queue.
+
+1. Insert
+2. Delete
+3. Display
+4. Exit
+Enter choice:
+2
+
+30 Deleted from queue.
+
+1. Insert
+2. Delete
+3. Display
+4. Exit
+Enter choice:
+2
+
+40 Deleted from queue.
+
+1. Insert
+2. Delete
+3. Display
+4. Exit
+Enter choice:
+2
+
+UNDERFLOW! Queue is Empty.
+
+1. Insert
+2. Delete
+3. Display
+4. Exit
+Enter choice:
+4
+ */