Circular Queue Implementation Using Array in DSA Python - Build from Scratch

Circular Queue Implementation Using Array

📖 Scenario: Imagine you are managing a small parking lot with a fixed number of parking spots arranged in a circle. Cars enter and leave in order, and when the last spot is reached, the next car goes back to the first spot if it is free. This is like a circular queue.

🎯 Goal: You will build a simple circular queue using an array to manage the parking spots. You will add cars, remove cars, and show the current state of the parking lot.

📋 What You'll Learn

Create an array to hold the queue elements with a fixed size

Use two pointers: front and rear to track the queue

Implement enqueue operation to add a car if space is available

Implement dequeue operation to remove a car if the queue is not empty

Print the current queue elements in order

💡 Why This Matters

🌍 Real World

Circular queues are used in real-world systems like traffic lights, CPU scheduling, and buffering data streams where resources are reused in a cycle.

💼 Career

Understanding circular queues helps in roles involving system design, embedded systems, and performance optimization where fixed-size buffers are common.

1

Create the Circular Queue Array and Pointers

Create a list called queue with 5 None elements to represent empty spots. Also create two variables front and rear and set both to -1 to indicate the queue is empty.

DSA Python

# Create queue list and initialize front and rear pointers
# Your code here

Hint

Use a list with 5 None values. Set front and rear to -1 to show the queue is empty.

2

Add a Car to the Circular Queue (Enqueue)

Create a function called enqueue(car) that adds car to the queue. Update rear to the next position in a circular way using modulo. If the queue is empty, set front to 0. Do not add if the queue is full (when next rear equals front).

DSA Python

queue = [None, None, None, None, None]
front = -1
rear = -1

# Define enqueue function to add a car
# Your code here

Hint

Check if queue is full by comparing next rear position with front. Use modulo to wrap around. Update front if queue was empty.

3

Remove a Car from the Circular Queue (Dequeue)

Create a function called dequeue() that removes and returns the car at front. If the queue becomes empty after removal, reset front and rear to -1. Otherwise, move front to the next position circularly.

DSA Python

queue = [None, None, None, None, None]
front = -1
rear = -1

def enqueue(car):
    global front, rear
    if (rear + 1) % len(queue) == front:
        return  # Queue is full, do nothing
    if front == -1:
        front = 0
    rear = (rear + 1) % len(queue)
    queue[rear] = car

# Define dequeue function to remove a car
# Your code here

Hint

Check if queue is empty first. Remove the car at front. If only one car was there, reset pointers. Otherwise, move front forward using modulo.

4

Print the Current Circular Queue

Write code to print the current elements in the queue from front to rear in order, separated by ' -> '. If the queue is empty, print 'Queue is empty'.

DSA Python

queue = [None, None, None, None, None]
front = -1
rear = -1

def enqueue(car):
    global front, rear
    if (rear + 1) % len(queue) == front:
        return  # Queue is full, do nothing
    if front == -1:
        front = 0
    rear = (rear + 1) % len(queue)
    queue[rear] = car

def dequeue():
    global front, rear
    if front == -1:
        return None  # Queue is empty
    car = queue[front]
    queue[front] = None
    if front == rear:
        front = -1
        rear = -1
    else:
        front = (front + 1) % len(queue)
    return car

# Print the queue elements from front to rear
# Your code here

Hint

Start from front and keep moving forward using modulo until you reach rear. Collect elements and join them with ' -> '.