Queue data structure

A queue is a sequence of people or objects waiting to be attended to. Some examples include a queue of people waiting at a counter, a queue of swimmers that are ready to dive in to a pool, and a queue of songs in a playlist:

Figure 10

Just like in a stack, there are two types of operations—one for inserting items into a queue, and one for removing items from a queue. When a person joins a queue, he or she must stand behind the last person. The operation of adding an item to a queue is called enqueue. The first person to be attended to in a queue is the person standing in the front. The operation to remove an item from a queue is called dequeue. Queue operations can be seen in the following diagram:

Figure 11

Since the first object inserted is the first one to be removed, this data structure is called first in first out (FIFO). In Python, we can use...