Queues
A Queue is a Linear Data Structure that follows the principle of FIFO or the First-In and First-Out Principle. The values can be added to the rear of the queue (Enqueue) and the values can be removed from the front of the queue (Dequeue). We will use a queue queue of fixed length 4. The various operations that can be performed on a Queue are :
-Enqueue: In this process, a value is put into the queue from the rear or the back of the queue.
def enqueue(): global queue if(len(queue)==4): print("Cannot perform action, queue is full") else: a = int(input("Enter value: ")) # adds value to the end (rear) of the queue queue.append(a) print(f"{a} added to rear of the queue") -Dequeue: In this process, a value is removed from the front of the queue.
def dequeue(): global queue if len(queue) == 0: print("Cannot perform action, queue is empty") else: print(f"Dequeued value: {queue[0]}") # removes the value from the front of the queue queue.pop(0) -Peek: In this process, the value at the front of the queue is displayed.
def peek(): global queue if len(queue) == 0: print("Queue is empty") else: print(f"Front value of Queue: {queue[0]}") -Rear: In this process, the value at the rear of the queue is displayed.
def rear(): global queue if len(queue) == 0: print("Queue is empty") else: print(f"Rear value of Queue: {queue[-1]}") -State_of_Queue: This function combines the operations is_empty(), which tells you whether or not the queue is empty, and is_full(), which tells you whether or not the queue is full. The function of the operation is:
def state_of_queue(): if len(queue) == 4: print("Queue is full") elif len(queue) == 0: print("Queue is empty") else: print("Queue is partially empty") 
To simulate the functioning of a queue, the complete code is given below:
import array as ar ## Global variables queue = ar.array('i', []) def enqueue(): global queue if(len(queue)==4): print("Cannot perform action, queue is full") else: a = int(input("Enter value: ")) # adds value to the end (rear) of the queue queue.append(a) print(f"{a} added to rear of the queue") def dequeue(): global queue if len(queue) == 0: print("Cannot perform action, queue is empty") else: print(f"Dequeued value: {queue[0]}") # removes the value from the front of the queue queue.pop(0) def peek(): global queue if len(queue) == 0: print("Queue is empty") else: print(f"Front value of Queue: {queue[0]}") def rear(): global queue if len(queue) == 0: print("Queue is empty") else: print(f"Rear value of Queue: {queue[-1]}") def state_of_queue(): if len(queue) == 4: print("Queue is full") elif len(queue) == 0: print("Queue is empty") else: print("Queue is partially empty") ## Driver Code while True: print("1.Enqueue\n2.Dequeue\n3.Peek\n4.Rear\n5.State of Queue\n6.Exit") ch = int(input("Enter choice: ")) if ch == 1: enqueue() elif ch == 2: dequeue() elif ch == 3: peek() elif ch == 4: rear() elif ch == 5: state_of_queue() else: break Another type of queue is called as a circular queue and can be read here
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