Hands-On Data Structures and Algorithms with Python - Second Edition

The enqueue operation

The enqueue operation adds an item to the queue. It uses the insert method of the list class to insert items (or data) at the front of the list. See the following code for the implementation of the enqueue method:

  def enqueue(self, data):     self.items.insert(0, data)   # Always insert items at index 0    self.size += 1               # increment the size of the queue by 1

It is important to note how we implement insertions in queues using list. The concept is that we add the items at index 0 in a list; it is the first position in an array or list. To understand the concept of how the queue works when we add items at index 0 in a list, consider the following diagram. We start with an empty list. Initially, we add an item 1 at index 0. Next, ...