Data Modelling & AI Data Structure & Algorithm

Input Restricted Queue

23 June 2025

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An input restricted queue is a special case of a double-ended queue where data can be inserted from one end(rear) but can be removed from both ends (front and rear). This kind of Queue does not follow FIFO(first in first out):

Input Restricted Queue

Operations on Input Restricted Queue:

Mainly the following three basic operations are performed on input restricted queue:

insertRear(): Adds an item at the rear of the queue.

deleteFront(): Deletes an item from the front of the queue.

deleteRear(): Deletes an item from rear of the queue.

In addition to above operations, following operations are also supported

getFront(): Gets the front item from the queue.

getRear(): Gets the last item from the queue.

isEmpty(): Checks whether queue is empty or not.

isFull(): Checks whether queue is full or not.

Below is the implementation of Input restricted queue:

C++

// C++ implementation of Input Restricted
// Queue using circular array
 
#include <iostream>
using namespace std;
 
// Maximum size of array or Input
// Restricted Queue
#define MAX 100
 
// A structure to represent a Input
// Restricted Queue
class Deque {
    int arr[MAX];
    int front;
    int rear;
    int size;
 
public:
    Deque(int size)
    {
        front = -1;
        rear = 0;
        this->size = size;
    }
 
    // Operations on Input
    // Restricted Queue
    void insertrear(int key);
    void deletefront();
    void deleterear();
    bool isFull();
    bool isEmpty();
    int getFront();
    int getRear();
};
 
// Checks whether Input Restricted
// Queue is full or not.
bool Deque::isFull()
{
    return ((front == 0 && rear == size - 1)
            || front == rear + 1);
}
 
// Checks whether Input Restricted
// Queue is empty or not.
bool Deque::isEmpty() { return (front == -1); }
 
// function to inset element at rear end
// of Input Restricted Queue
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
// Input Restricted Queue
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
// Input Restricted Queue
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 Input
// Restricted Queue
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
// Input Restricted Queue
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 << "insert element at rear end : 15 \n";
    dq.insertrear(15);
 
    cout << "Get rear element : "
         << " " << dq.getRear() << endl;
 
    dq.deleterear();
    cout << "After delete rear element new rear"
         << " become : " << dq.getRear() << endl;
 
    cout << "Get front element : " << dq.getFront() << endl;
 
    dq.deletefront();
 
    cout << "After delete front element new "
         << "front become : " << dq.getFront() << endl;
    return 0;
}

Java

// Java program for the above approach
// Queue using circular array
 
// A structure to represent a Input
// Restricted Queue
class Deque {
 
    int[] arr;
    int front;
    int rear;
    int size;
 
    public Deque(int size)
    {
        this.size = size;
        arr = new int[size];
        front = -1;
        rear = 0;
    }
    // Operations on Input
    // Restricted Queue
 
    // Checks whether Input Restricted
    // Queue is full or not.
    public boolean isFull()
    {
        return (front == 0 && rear == size - 1)
            || front == rear + 1;
    }
    // Checks whether Input Restricted
    // Queue is empty or not.
    public boolean isEmpty() { return front == -1; }
    // function to inset element at rear end
    // of Input Restricted Queue
    public void insertRear(int key)
    {
        if (isFull()) {
            System.out.println(" Overflow");
            return;
        }
 
        if (front == -1) {
            front = 0;
            rear = 0;
        }
        else if (rear == size - 1) {
            rear = 0;
        }
        else {
            rear++;
        }
        arr[rear] = key;
    }
    // Deletes element at front end of
    // Input Restricted Queue
    public void deleteFront()
    {
        if (isEmpty()) {
            System.out.println("Queue Underflow");
            return;
        }
 
        if (front == rear) {
            front = -1;
            rear = -1;
        }
        else if (front == size - 1) {
            front = 0;
        }
        else {
            front++;
        }
    }
    // Delete element at rear end of
    // Input Restricted Queue
    public void deleteRear()
    {
        if (isEmpty()) {
            System.out.println(" Underflow");
            return;
        }
 
        if (front == rear) {
            front = -1;
            rear = -1;
        }
        else if (rear == 0) {
            rear = size - 1;
        }
        else {
            rear--;
        }
    }
    // Returns front element of Input
    // Restricted Queue
    public int getFront()
    {
        if (isEmpty()) {
            System.out.println(" Underflow");
            return -1;
        }
        return arr[front];
    }
    // Function return rear element of
    // Input Restricted Queue
    public int getRear()
    {
        if (isEmpty() || rear < 0) {
            System.out.println(" Underflow");
            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(
            "Insert element at rear end : 15 ");
        dq.insertRear(15);
 
        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("Get front element : "
                           + dq.getFront());
 
        dq.deleteFront();
        System.out.println(
            "After delete front element new front become :"
            + dq.getFront());
    }
}

C#

// C# program for the above approach
// Queue using circular array
using System;
 
// A structure to represent a Input
// Restricted Queue
public class Deque {
 
    int[] arr;
    int front;
    int rear;
    int size;
 
    public Deque(int size)
    {
        this.size = size;
        arr = new int[size];
        front = -1;
        rear = 0;
    }
    // Operations on Input
    // Restricted Queue
 
    // Checks whether Input Restricted
    // Queue is full or not.
    public bool isFull()
    {
        return (front == 0 && rear == size - 1)
            || front == rear + 1;
    }
   
    // Checks whether Input Restricted
    // Queue is empty or not.
    public bool isEmpty() { return front == -1; }
   
    // function to inset element at rear end
    // of Input Restricted Queue
    public void insertRear(int key)
    {
        if (isFull()) {
            Console.WriteLine(" Overflow");
            return;
        }
 
        if (front == -1) {
            front = 0;
            rear = 0;
        }
        else if (rear == size - 1) {
            rear = 0;
        }
        else {
            rear++;
        }
        arr[rear] = key;
    }
    // Deletes element at front end of
    // Input Restricted Queue
    public void deleteFront()
    {
        if (isEmpty()) {
            Console.WriteLine("Queue Underflow");
            return;
        }
 
        if (front == rear) {
            front = -1;
            rear = -1;
        }
        else if (front == size - 1) {
            front = 0;
        }
        else {
            front++;
        }
    }
    // Delete element at rear end of
    // Input Restricted Queue
    public void deleteRear()
    {
        if (isEmpty()) {
            Console.WriteLine(" Underflow");
            return;
        }
 
        if (front == rear) {
            front = -1;
            rear = -1;
        }
        else if (rear == 0) {
            rear = size - 1;
        }
        else {
            rear--;
        }
    }
   
    // Returns front element of Input
    // Restricted Queue
    public int getFront()
    {
        if (isEmpty()) {
            Console.WriteLine(" Underflow");
            return -1;
        }
        return arr[front];
    }
   
    // Function return rear element of
    // Input Restricted Queue
    public int getRear()
    {
        if (isEmpty() || rear < 0) {
            Console.WriteLine(" Underflow");
            return -1;
        }
        return arr[rear];
    }
 
    static public void Main()
    {
 
        // Code
        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(
            "Insert element at rear end : 15 ");
        dq.insertRear(15);
 
        Console.WriteLine("Get rear element : "
                          + dq.getRear());
 
        dq.deleteRear();
 
        Console.WriteLine(
            "After delete rear element new rear become : "
            + dq.getRear());
        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 lokesh.

Python3

class Deque:
    def __init__(self, size):
        self.size = size
        self.arr = [0] * size
        self.front = -1
        self.rear = 0
 
    def is_full(self):
        return (self.front == 0 and self.rear == self.size - 1) or self.front == self.rear + 1
 
    def is_empty(self):
        return self.front == -1
 
    def insert_rear(self, key):
        if self.is_full():
            print("Overflow")
            return
        if self.front == -1:
            self.front = 0
            self.rear = 0
        elif self.rear == self.size - 1:
            self.rear = 0
        else:
            self.rear += 1
        self.arr[self.rear] = key
 
    def delete_front(self):
        if self.is_empty():
            print("Queue Underflow")
            return
        if self.front == self.rear:
            self.front = -1
            self.rear = -1
        elif self.front == self.size - 1:
            self.front = 0
        else:
            self.front += 1
 
    def delete_rear(self):
        if self.is_empty():
            print("Underflow")
            return
        if self.front == self.rear:
            self.front = -1
            self.rear = -1
        elif self.rear == 0:
            self.rear = self.size - 1
        else:
            self.rear -= 1
 
    def get_front(self):
        if self.is_empty():
            print("Underflow")
            return -1
        return self.arr[self.front]
 
    def get_rear(self):
        if self.is_empty() or self.rear < 0:
            print("Underflow")
            return -1
        return self.arr[self.rear]
 
if __name__ == "__main__":
    dq = Deque(5)
    print("Insert element at rear end : 5 ")
    dq.insert_rear(5)
    print("Insert element at rear end : 10 ")
    dq.insert_rear(10)
    print("Insert element at rear end : 15 ")
    dq.insert_rear(15)
    print("Get rear element : ", dq.get_rear())
    dq.delete_rear()
    print("After delete rear element new rear become : ", dq.get_rear())
    print("Get front element : ", dq.get_front())
    dq.delete_front()
    print("After delete front element new front become : ", dq.get_front())

Javascript

// JavaScript program for the above approach
// Queue using circular array
  
// A structure to represent a Input
// Restricted Queue
class Deque {
    constructor(size) {
        this.arr = new Array(size);
        this.front = -1;
        this.rear = 0;
        this.size = size;
    }
    // Operations on Input
    // Restricted Queue
  
    // Checks whether Input Restricted
    // Queue is full or not.
    isFull() {
        return (this.front === 0 && this.rear === this.size - 1) || this.front === this.rear + 1;
    }
 
    // Checks whether Input Restricted
    // Queue is empty or not.
    isEmpty() {
        return this.front === -1;
    }
 
    // function to inset element at rear end
    // of Input Restricted Queue
    insertrear(key) {
        if (this.isFull()) {
            console.log("Overflow");
            return;
        }
        if (this.front === -1) {
            this.front = 0;
            this.rear = 0;
        }
        else if (this.rear === this.size - 1) {
            this.rear = 0;
        }
        else {
            this.rear = this.rear + 1;
        }
        this.arr[this.rear] = key;
    }
 
    // Deletes element at front end of
    // Input Restricted Queue
    deletefront() {
        if (this.isEmpty()) {
            console.log("Queue Underflow");
            return;
        }
        if (this.front === this.rear) {
            this.front = -1;
            this.rear = -1;
        }
        else if (this.front === this.size - 1) {
            this.front = 0;
        }
        else {
            this.front = this.front + 1;
        }
    }
 
    // Delete element at rear end of
    // Input Restricted Queue
    deleterear() {
        if (this.isEmpty()) {
            console.log("Underflow");
            return;
        }
        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 Input
    // Restricted Queue
    getFront() {
        if (this.isEmpty()) {
            console.log("Underflow");
            return -1;
        }
        return this.arr[this.front];
    }
 
    // Function return rear element of
    // Input Restricted Queue
    getRear() {
        if (this.isEmpty() || this.rear < 0) {
            console.log("Underflow");
            return -1;
        }
        return this.arr[this.rear];
    }
}
 
// Driver code
 
// Function calls
const dq = new Deque(5);
console.log("Insert element at rear end : 5");
dq.insertrear(5);
console.log("Insert element at rear end : 10");
dq.insertrear(10);
console.log("Insert element at rear end : 15");
dq.insertrear(15);
console.log("Get rear element : ", dq.getRear());
dq.deleterear();
console.log("After delete rear element new rear become : ", dq.getRear());
console.log("Get front element : ", dq.getFront());
dq.deletefront();
console.log("After delete front element new front become : ", dq.getFront());
 
// This code is contributed by Prasad Kandekar(prasad264)

Output

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

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

Need to implement input restricted queue:

This queue is used when it is necessary to consume data in FIFO order but it is necessary to discard recently added data for a variety of reasons, such as useless data, performance issues, etc.
It is needed when we have to inhibit insertion from the front of the deque.
It is used in job scheduling algorithms.

Advantages of Input Restricted Queue:

Security of the system by restricting the insert method of the queue at the front.

Disadvantages of Input Restricted Queue:

Can’t provide the added functionality in comparison to Deque.

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Input Restricted Queue

Operations on Input Restricted Queue:

C++

Java

C#

Python3

Javascript

Need to implement input restricted queue:

Advantages of Input Restricted Queue:

Disadvantages of Input Restricted Queue:

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