Since our queue is currently empty, let’s add to it! To enqueue literally means “add to the queue”. In creating the enqueue() method, that’s exactly what we’ll do.
When adding a new node to the queue, the new node is always added to the end of the queue.
- If the queue is empty, the new node becomes the head and tail of the queue. (Imagine only one person is in line).
- If the queue has at least one other node, the new node becomes the new tail. (Someone joins a line of people).
We can put this into action by creating the enqueue() method of the Queue struct.
Instructions
Within the Queue struct, declare a method that does not return a value, called enqueue(). It which should accept a parameter for data of type, String, and allow for the argument label to be omitted.
Since we expect this method to alter the queue, don’t forget to add the mutating keyword at the start of the method.
Create a newNode constant that stores an instance of a new Node with the data parameter name passed in for the data property.
Now let’s check if the tail is nil. If it is:
- Set the
headto be thenewNode - Set the
tailto be thenewNode - Add an empty
return
Finally, outside of the guard statement, we want to update the last node’s pointer to the next node and update the tail.
- Set the
lastNode‘snextnode to be the new node - Set the
tailasnewNode