Queue

The most recently added item in the queue must wait at the end of the collection. The item that has been in the collection the longest is at the front. This ordering principle is sometimes called FIFO, first-in first-out. It is also known as “first-come first-served.”

Queue() creates a new queue that is empty. It needs no parameters and returns an empty queue.

enqueue(item) adds a new item to the rear of the queue. It needs the item and returns nothing.

dequeue() removes the front item from the queue. It needs no parameters and returns the item. The queue is modified.

isEmpty() tests to see whether the queue is empty. It needs no parameters and returns a boolean value.

size() returns the number of items in the queue. It needs no parameters and returns an integer.

Implementing a Queue in Python

class Queue:    def __init__(self):        self.items = []    def isEmpty(self):        return self.items == []    def enqueue(self, item):        self.items.insert(0,item)        #Insert an item at a given position.        # The first argument is the index of the element before which to insert, so a.insert(0, x)        # inserts at the front of the list, and a.insert(len(a), x) is equivalent to a.append(x).    def dequeue(self):        return self.items.pop()    def size(self):        return len(self.items)q=Queue()q.enqueue(4)q.enqueue('dog')q.dequeue()print(q.size())

Q-33: Suppose you have the following series of queue operations.
q = Queue()
q.enqueue(‘hello’)
q.enqueue(‘dog’)
q.enqueue(3)
q.dequeue()
What items are left on the queue?
‘dog’, 3