Implementation of Deque using circular array

Implement a deque Using a circular array:

Deque or Double Ended Queue is a generalized version of the Queue data structure that allows insert and delete at both ends

Operations on Deque:

Mainly the following four basic operations are performed on queue: 

• insertFront(): Adds an item at the front of Deque.
• insertRear(): Adds an item at the rear of Deque. 
• deleteFront(): Deletes an item from front of Deque. 
• deleteRear(): Deletes an item from rear of Deque.

In addition to above operations, following operations are also supported 

• getFront(): Gets the front item from queue. 
• getRear(): Gets the last item from queue. 
• isEmpty(): Checks whether Deque is empty or not. 
• isFull(): Checks whether Deque is full or not. 
  

Circular array implementation of Deque:

For implementing deque, we need to keep track of two indices, front, and rear. We enqueue(push) an item at the rear or the front end of the dequeue and dequeue(pop) an item from both the rear and the front end. 

Working: 

Create an empty array ‘arr’ of size N
initialize front = -1 , rear = 0
Inserting the First element in the deque, at either front or rear will lead to the same result:

Note: After inserting Front Points at 0 and Rear points at 0 

Insert Elements at the Rear end of Deque:

a). First we check deque if Full or Not 

b). IF Rear == Size-1 
     then reinitialize Rear = 0 ;
     Else increment Rear by ‘1’
     and push current key into Arr[ rear ] = key 
     Front remain same.      

Insert Elements at the Front end  of Deque:

a). First we check deque if Full or Not

b). IF Front == 0 || initial position, move Front
     to points last index of array
     front = size – 1
     Else decremented front by ‘1’ and push 
     current key into Arr[ Front] = key 
     Rear remain same

Delete Element From Rear end of Deque: 

First Check deque is Empty or Not

If deque has only one element
front = -1 ; rear =-1;

Else IF Rear points to the first index of array
it’s means we have to move rear to points 
last index [ now first inserted element at 
front end become rear end ]  

rear = size-1;
Else || decrease rear by ‘1’  rear = rear-1;

Delete Element From the Front end of Deque:

a). first Check deque is Empty or Not

b).  If deque has only one element
      front = -1 ; rear =-1 ;

Else IF front points to the last index of the array
it’s means we have no more elements in array so 
we move front to points first index of array
front = 0 ;

Else || increment Front by ‘1’  
front = front+1;

Below is the implementation of the above methods: 

C++

// C++ implementation of De-queue using circular
// array
#include <iostream>
using namespace std;

// Maximum size of array or Dequeue
#define MAX 100

// A structure to represent a Deque
class Deque {
    int arr[MAX];
    int front;
    int rear;
    int size;

public:
    Deque(int size)
    {
        front = -1;
        rear = 0;
        this->size = size;
    }

    // Operations on Deque:
    void insertfront(int key);
    void insertrear(int key);
    void deletefront();
    void deleterear();
    bool isFull();
    bool isEmpty();
    int getFront();
    int getRear();
};

// Checks whether Deque is full or not.
bool Deque::isFull()
{
    return ((front == 0 && rear == size - 1)
            || front == rear + 1);
}

// Checks whether Deque is empty or not.
bool Deque::isEmpty() { return (front == -1); }

// Inserts an element at front
void Deque::insertfront(int key)
{
    // check whether Deque if  full or not
    if (isFull()) {
        cout << "Overflow\n" << endl;
        return;
    }

    // If queue is initially empty
    if (front == -1) {
        front = 0;
        rear = 0;
    }

    // front is at first position of queue
    else if (front == 0)
        front = size - 1;

    else // decrement front end by '1'
        front = front - 1;

    // insert current element into Deque
    arr[front] = key;
}

// function to inset element at rear end
// of Deque.
void Deque ::insertrear(int key)
{
    if (isFull()) {
        cout << " Overflow\n " << endl;
        return;
    }

    // If queue is initially empty
    if (front == -1) {
        front = 0;
        rear = 0;
    }

    // rear is at last position of queue
    else if (rear == size - 1)
        rear = 0;

    // increment rear end by '1'
    else
        rear = rear + 1;

    // insert current element into Deque
    arr[rear] = key;
}

// Deletes element at front end of Deque
void Deque ::deletefront()
{
    // check whether Deque is empty or not
    if (isEmpty()) {
        cout << "Queue Underflow\n" << endl;
        return;
    }

    // Deque has only one element
    if (front == rear) {
        front = -1;
        rear = -1;
    }
    else
        // back to initial position
        if (front == size - 1)
        front = 0;

    else // increment front by '1' to remove current
        // front value from Deque
        front = front + 1;
}

// Delete element at rear end of Deque
void Deque::deleterear()
{
    if (isEmpty()) {
        cout << " Underflow\n" << endl;
        return;
    }

    // Deque has only one element
    if (front == rear) {
        front = -1;
        rear = -1;
    }
    else if (rear == 0)
        rear = size - 1;
    else
        rear = rear - 1;
}

// Returns front element of Deque
int Deque::getFront()
{
    // check whether Deque is empty or not
    if (isEmpty()) {
        cout << " Underflow\n" << endl;
        return -1;
    }
    return arr[front];
}

// function return rear element of Deque
int Deque::getRear()
{
    // check whether Deque is empty or not
    if (isEmpty() || rear < 0) {
        cout << " Underflow\n" << endl;
        return -1;
    }
    return arr[rear];
}

// Driver code
int main()
{
    Deque dq(5);

      // Function calls
    cout << "Insert element at rear end  : 5 \n";
    dq.insertrear(5);

    cout << "insert element at rear end : 10 \n";
    dq.insertrear(10);

    cout << "get rear element "
         << " " << dq.getRear() << endl;

    dq.deleterear();
    cout << "After delete rear element new rear"
         << " become " << dq.getRear() << endl;

    cout << "inserting element at front end \n";
    dq.insertfront(15);

    cout << "get front element "
         << " " << dq.getFront() << endl;

    dq.deletefront();

    cout << "After delete front element new "
         << "front become " << dq.getFront() << endl;
    return 0;
}

Java

// Java implementation of De-queue using circular
// array

// A structure to represent a Deque
class Deque {
    static final int MAX = 100;
    int arr[];
    int front;
    int rear;
    int size;

    public Deque(int size)
    {
        arr = new int[MAX];
        front = -1;
        rear = 0;
        this.size = size;
    }

    /*// Operations on Deque:
    void  insertfront(int key);
    void  insertrear(int key);
    void  deletefront();
    void  deleterear();
    bool  isFull();
    bool  isEmpty();
    int  getFront();
    int  getRear();*/

    // Checks whether Deque is full or not.
    boolean isFull()
    {
        return ((front == 0 && rear == size - 1)
                || front == rear + 1);
    }

    // Checks whether Deque is empty or not.
    boolean isEmpty() { return (front == -1); }

    // Inserts an element at front
    void insertfront(int key)
    {
        // check whether Deque if  full or not
        if (isFull()) {
            System.out.println("Overflow");
            return;
        }

        // If queue is initially empty
        if (front == -1) {
            front = 0;
            rear = 0;
        }

        // front is at first position of queue
        else if (front == 0)
            front = size - 1;

        else // decrement front end by '1'
            front = front - 1;

        // insert current element into Deque
        arr[front] = key;
    }

    // function to inset element at rear end
    // of Deque.
    void insertrear(int key)
    {
        if (isFull()) {
            System.out.println(" Overflow ");
            return;
        }

        // If queue is initially empty
        if (front == -1) {
            front = 0;
            rear = 0;
        }

        // rear is at last position of queue
        else if (rear == size - 1)
            rear = 0;

        // increment rear end by '1'
        else
            rear = rear + 1;

        // insert current element into Deque
        arr[rear] = key;
    }

    // Deletes element at front end of Deque
    void deletefront()
    {
        // check whether Deque is empty or not
        if (isEmpty()) {
            System.out.println("Queue Underflow\n");
            return;
        }

        // Deque has only one element
        if (front == rear) {
            front = -1;
            rear = -1;
        }
        else
            // back to initial position
            if (front == size - 1)
            front = 0;

        else // increment front by '1' to remove current
            // front value from Deque
            front = front + 1;
    }

    // Delete element at rear end of Deque
    void deleterear()
    {
        if (isEmpty()) {
            System.out.println(" Underflow");
            return;
        }

        // Deque has only one element
        if (front == rear) {
            front = -1;
            rear = -1;
        }
        else if (rear == 0)
            rear = size - 1;
        else
            rear = rear - 1;
    }

    // Returns front element of Deque
    int getFront()
    {
        // check whether Deque is empty or not
        if (isEmpty()) {
            System.out.println(" Underflow");
            return -1;
        }
        return arr[front];
    }

    // function return rear element of Deque
    int getRear()
    {
        // check whether Deque is empty or not
        if (isEmpty() || rear < 0) {
            System.out.println(" Underflow\n");
            return -1;
        }
        return arr[rear];
    }

    // Driver code
    public static void main(String[] args)
    {

        Deque dq = new Deque(5);

          // Function calls
        System.out.println(
            "Insert element at rear end  : 5 ");
        dq.insertrear(5);

        System.out.println(
            "insert element at rear end : 10 ");
        dq.insertrear(10);

        System.out.println("get rear element : "
                           + dq.getRear());

        dq.deleterear();
        System.out.println(
            "After delete rear element new rear become : "
            + dq.getRear());

        System.out.println(
            "inserting element at front end");
        dq.insertfront(15);

        System.out.println("get front element: "
                           + dq.getFront());

        dq.deletefront();

        System.out.println(
            "After delete front element new front become : "
            + +dq.getFront());
    }
}

Python3

# Python implementation of De-queue using circular
# array

# A structure to represent a Deque
MAX = 100


class Deque:
    def __init__(self, size):
        self.arr = [0] * MAX
        self.front = -1
        self.rear = 0
        self.size = size

    ''' Operations on Deque:
    void  insertfront(int key);
    void  insertrear(int key);
    void  deletefront();
    void  deleterear();
    bool  isFull();
    bool  isEmpty();
    int  getFront();
    int  getRear(); '''

    # Checks whether Deque is full or not.
    def isFull(self):
        return ((self.front == 0 and self.rear == self.size-1) or self.front == self.rear + 1)

    # Checks whether Deque is empty or not.

    def isEmpty(self):
        return (self.front == -1)

    # Inserts an element at front
    def insertfront(self, key):

        # check whether Deque if  full or not
        if (self.isFull()):
            print("Overflow")
            return

        # If queue is initially empty
        if (self.front == -1):
            self.front = 0
            self.rear = 0

        # front is at first position of queue
        elif (self.front == 0):
            self.front = self.size - 1

        else:  # decrement front end by '1'
            self.front = self.front-1

        # insert current element into Deque
        self.arr[self.front] = key

    # function to inset element at rear end
    # of Deque.

    def insertrear(self, key):
        if (self.isFull()):
            print(" Overflow")
            return

        # If queue is initially empty
        if (self.front == -1):
            self.front = 0
            self.rear = 0

        # rear is at last position of queue
        elif (self.rear == self.size-1):
            self.rear = 0

        # increment rear end by '1'
        else:
            self.rear = self.rear+1

        # insert current element into Deque
        self.arr[self.rear] = key

    # Deletes element at front end of Deque

    def deletefront(self):
        # check whether Deque is empty or not
        if (self.isEmpty()):
            print("Queue Underflow")
            return

        # Deque has only one element
        if (self.front == self.rear):
            self.front = -1
            self.rear = -1

        else:
            # back to initial position
            if (self.front == self.size - 1):
                self.front = 0

            else:  # increment front by '1' to remove current
                # front value from Deque
                self.front = self.front+1

    # Delete element at rear end of Deque

    def deleterear(self):
        if (self.isEmpty()):
            print(" Underflow")
            return

        # Deque has only one element
        if (self.front == self.rear):
            self.front = -1
            self.rear = -1

        elif (self.rear == 0):
            self.rear = self.size-1
        else:
            self.rear = self.rear-1

    # Returns front element of Deque

    def getFront(self):
        # check whether Deque is empty or not
        if (self.isEmpty()):
            print(" Underflow")
            return -1

        return self.arr[self.front]

    # function return rear element of Deque

    def getRear(self):
        # check whether Deque is empty or not
        if(self.isEmpty() or self.rear < 0):
            print(" Underflow")
            return -1

        return self.arr[self.rear]


# Driver code
if __name__ == "__main__":
  dq = Deque(5)

  # Function calls
  print("Insert element at rear end  : 5 ")
  dq.insertrear(5)

  print("insert element at rear end : 10 ")
  dq.insertrear(10)

  print(f"get rear element : {dq.getRear()}")

  dq.deleterear()
  print(f"After delete rear element new rear become : {dq.getRear()}")

  print("inserting element at front end")
  dq.insertfront(15)

  print(f"get front element: {dq.getFront()}")

  dq.deletefront()

  print(f"After delete front element new front become : {dq.getFront()}")

# This code is contributed by _saurabh_jaiswal

C#

// C# implementation of De-queue using circular
// array
using System;

// A structure to represent a Deque
public class Deque {
    static readonly int MAX = 100;
    int[] arr;
    int front;
    int rear;
    int size;

    public Deque(int size)
    {
        arr = new int[MAX];
        front = -1;
        rear = 0;
        this.size = size;
    }

    /*// Operations on Deque:
    void  insertfront(int key);
    void  insertrear(int key);
    void  deletefront();
    void  deleterear();
    bool  isFull();
    bool .Count!=0;
    int  getFront();
    int  getRear();*/

    // Checks whether Deque is full or not.
    bool isFull()
    {
        return ((front == 0 && rear == size - 1)
                || front == rear + 1);
    }

    // Checks whether Deque is empty or not.
    bool isEmpty() { return (front == -1); }

    // Inserts an element at front
    void insertfront(int key)
    {

        // check whether Deque if  full or not
        if (isFull()) {
            Console.WriteLine("Overflow");
            return;
        }

        // If queue is initially empty
        if (front == -1) {
            front = 0;
            rear = 0;
        }

        // front is at first position of queue
        else if (front == 0)
            front = size - 1;

        else // decrement front end by '1'
            front = front - 1;

        // insert current element into Deque
        arr[front] = key;
    }

    // function to inset element at rear end
    // of Deque.
    void insertrear(int key)
    {
        if (isFull()) {
            Console.WriteLine(" Overflow ");
            return;
        }

        // If queue is initially empty
        if (front == -1) {
            front = 0;
            rear = 0;
        }

        // rear is at last position of queue
        else if (rear == size - 1)
            rear = 0;

        // increment rear end by '1'
        else
            rear = rear + 1;

        // insert current element into Deque
        arr[rear] = key;
    }

    // Deletes element at front end of Deque
    void deletefront()
    {

        // check whether Deque is empty or not
        if (isEmpty()) {
            Console.WriteLine("Queue Underflow\n");
            return;
        }

        // Deque has only one element
        if (front == rear) {
            front = -1;
            rear = -1;
        }
        else
            // back to initial position
            if (front == size - 1)
            front = 0;

        else // increment front by '1' to remove current
            // front value from Deque
            front = front + 1;
    }

    // Delete element at rear end of Deque
    void deleterear()
    {
        if (isEmpty()) {
            Console.WriteLine(" Underflow");
            return;
        }

        // Deque has only one element
        if (front == rear) {
            front = -1;
            rear = -1;
        }
        else if (rear == 0)
            rear = size - 1;
        else
            rear = rear - 1;
    }

    // Returns front element of Deque
    int getFront()
    {
        // check whether Deque is empty or not
        if (isEmpty()) {
            Console.WriteLine(" Underflow");
            return -1;
        }
        return arr[front];
    }

    // function return rear element of Deque
    int getRear()
    {

        // check whether Deque is empty or not
        if (isEmpty() || rear < 0) {
            Console.WriteLine(" Underflow\n");
            return -1;
        }
        return arr[rear];
    }

    // Driver code
    public static void Main(String[] args)
    {

        Deque dq = new Deque(5);

          // Function calls
        Console.WriteLine(
            "Insert element at rear end  : 5 ");
        dq.insertrear(5);
        Console.WriteLine(
            "insert element at rear end : 10 ");
        dq.insertrear(10);
        Console.WriteLine("get rear element : "
                          + dq.getRear());
        dq.deleterear();
        Console.WriteLine(
            "After delete rear element new rear become : "
            + dq.getRear());
        Console.WriteLine("inserting element at front end");
        dq.insertfront(15);
        Console.WriteLine("get front element: "
                          + dq.getFront());
        dq.deletefront();
        Console.WriteLine(
            "After delete front element new front become : "
            + +dq.getFront());
    }
}

// This code is contributed by aashish1995

Javascript

<script>
// Javascript implementation of De-queue using circular
// array

// A structure to represent a Deque
let MAX = 100;
class Deque
{
    constructor(size)
    {
        this.arr = new Array(MAX);
        this.front = -1;
        this.rear = 0;
        this.size = size;
    }

    /*// Operations on Deque:
    void  insertfront(int key);
    void  insertrear(int key);
    void  deletefront();
    void  deleterear();
    bool  isFull();
    bool  isEmpty();
    int  getFront();
    int  getRear();*/

    // Checks whether Deque is full or not.
    isFull()
    {
        return ((this.front == 0 && this.rear == this.size-1)||
            this.front == this.rear+1);
    }

    // Checks whether Deque is empty or not.
    isEmpty ()
    {
        return (this.front == -1);
    }

    // Inserts an element at front
    insertfront(key)
    {
        // check whether Deque if  full or not
        if (this.isFull())
        {
            document.write("Overflow<br>");
            return;
        }

        // If queue is initially empty
        if (this.front == -1)
        {
            this.front = 0;
            this.rear = 0;
        }

        // front is at first position of queue
        else if (this.front == 0)
            this.front = this.size - 1 ;

        else // decrement front end by '1'
            this.front = this.front-1;

        // insert current element into Deque
        this.arr[this.front] = key ;
    }

    // function to inset element at rear end
    // of Deque.
    insertrear(key)
    {
        if (this.isFull())
        {
            document.write(" Overflow <br>");
            return;
        }

        // If queue is initially empty
        if (this.front == -1)
        {
            this.front = 0;
            this.rear = 0;
        }

        // rear is at last position of queue
        else if (this.rear == this.size-1)
            this.rear = 0;

        // increment rear end by '1'
        else
            this.rear = this.rear+1;

        // insert current element into Deque
        this.arr[this.rear] = key ;
    }

    // Deletes element at front end of Deque
    deletefront()
    {
        // check whether Deque is empty or not
        if (this.isEmpty())
        {
            document.write("Queue Underflow<br>");
            return ;
        }

        // Deque has only one element
        if (this.front == this.rear)
        {
            this.front = -1;
            this.rear = -1;
        }
        else
            // back to initial position
            if (this.front == this.size -1)
                this.front = 0;

            else // increment front by '1' to remove current
                // front value from Deque
                this.front = this.front+1;
    }

    // Delete element at rear end of Deque
    deleterear()
    {
        if (this.isEmpty())
        {
            document.write(" Underflow<br>");
            return ;
        }

        // Deque has only one element
        if (this.front == this.rear)
        {
            this.front = -1;
            this.rear = -1;
        }
        else if (this.rear == 0)
            this.rear = this.size-1;
        else
            this.rear = this.rear-1;
    }

    // Returns front element of Deque
    getFront()
    {
        // check whether Deque is empty or not
        if (this.isEmpty())
        {
            document.write(" Underflow<br>");
            return -1 ;
        }
        return this.arr[this.front];
    }

    // function return rear element of Deque
    getRear()
    {
        // check whether Deque is empty or not
        if(this.isEmpty() || this.rear < 0)
        {
            document.write(" Underflow<br>");
            return -1 ;
        }
        return this.arr[this.rear];
    }

}

// Driver program to test above function
let dq = new Deque(5);

document.write("Insert element at rear end  : 5 <br>");
dq.insertrear(5);

document.write("insert element at rear end : 10 <br>");
dq.insertrear(10);

document.write("get rear element : "+ dq.getRear()+"<br>");

dq.deleterear();
document.write("After delete rear element new rear become : " +
                   dq.getRear()+"<br>");

document.write("inserting element at front end<br>");
dq.insertfront(15);

document.write("get front element: " +dq.getFront()+"<br>");

dq.deletefront();

document.write("After delete front element new front become : " +
                   +  dq.getFront()+"<br>");

// This code is contributed by avanitrachhadiya2155
</script>

Output

Insert element at rear end  : 5 
insert element at rear end : 10 
get rear element  10
After delete rear element new rear become 5
inserting element at front end 
get front element  15
After delete front element new front become 5

Time Complexity: O(N)
Auxiliary Space: O(N)

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