Stacks and Queues Introduction to Computing Science and Programming I

Data Structures Data structures are different structures that can be used to store data. Different structures will organize it differently causing differences in how the data is accessed and changed. Data structures are different structures that can be used to store data. Different structures will organize it differently causing differences in how the data is accessed and changed. The only data structure we’ve used in Python is the list. The only data structure we’ve used in Python is the list.

Abstract Data Type We’re going to talk about a couple abstract data types. We’re only going to look at them in a very general, abstract way. We won’t worry about details of how to implement the structures in Python. We will only discuss how the data is organized and what operations can be performed on it. We’re going to talk about a couple abstract data types. We’re only going to look at them in a very general, abstract way. We won’t worry about details of how to implement the structures in Python. We will only discuss how the data is organized and what operations can be performed on it. The structures can be used in any programming language. The structures can be used in any programming language.

Queues A queue is a simple data structure that is works similar to a line of people (a queue) waiting to be helped by a cashier. A queue is a simple data structure that is works similar to a line of people (a queue) waiting to be helped by a cashier. You can only add or remove items one at a time. You can only add or remove items one at a time. It is a First In First Out, FIFO data structure. The first item you put in will be the first item that leaves the queue. It is a First In First Out, FIFO data structure. The first item you put in will be the first item that leaves the queue.

Queues \ / Entrance -> -> Exit / \ Every queue has to basic operations. Every queue has to basic operations. queue(Item) adds the item to the queue queue(Item) adds the item to the queue dequeue() removes an item from the queue dequeue() removes an item from the queue Some operations that many queues have, but aren’t required. Some operations that many queues have, but aren’t required. size() number of elements in the queue size() number of elements in the queue isEmpty() check whether there are any items isEmpty() check whether there are any items peek() Look at the next item to be removed without removing it peek() Look at the next item to be removed without removing it

Queues \ / Entrance -> > Exit / \ This is what the queue would look like after the following operations. This is what the queue would look like after the following operations. queue(8) queue(8) queue(10) queue(10) queue(5) queue(5) If the items we’re removed using the dequeue operation, they would be returned in the order they were put it, 8, then 10, and finally 5. If the items we’re removed using the dequeue operation, they would be returned in the order they were put it, 8, then 10, and finally 5.

Queues Remember that these queues and any other structure can store numbers, strings, or objects of any kind. Remember that these queues and any other structure can store numbers, strings, or objects of any kind. Applications of the queue have to do with resource management and requests. For example if you send several documents to be printed, they will be put in a queue before being printed one at a time in the order they were added. Applications of the queue have to do with resource management and requests. For example if you send several documents to be printed, they will be put in a queue before being printed one at a time in the order they were added.

Stacks A stack is a simple data structure that works similarly to a stack of papers. You can only add elements to the top and also only remove them from the top. A stack is a simple data structure that works similarly to a stack of papers. You can only add elements to the top and also only remove them from the top. This makes it a Last In First Out, LIFO, structure because the last item added will be the first one removed. This makes it a Last In First Out, LIFO, structure because the last item added will be the first one removed.

Stacks Enter -> -> Exit Enter -> -> Exit | | Every stack has to basic operations. Every stack has to basic operations. push(Item) adds the item to the top of the stack, “pushing” the others down push(Item) adds the item to the top of the stack, “pushing” the others down pop() removes an item from the top of the stack pop() removes an item from the top of the stack Some operations that many stacks have, but aren’t required. Some operations that many stacks have, but aren’t required. size() number of elements in the stack size() number of elements in the stack isEmpty() check whether there are any items isEmpty() check whether there are any items peek() Look at the next item to be removed without removing it peek() Look at the next item to be removed without removing it

Stacks Enter -> -> Exit Enter -> -> Exit | 5 | | 10| | 8| This is what the stack would look like after the following operations. This is what the stack would look like after the following operations. push(8) push(8) push(10) push(10) push(5) push(5) If the items we’re removed using the pop operation, they would be returned in the reverse of the order they were put it, 5, then 10, and finally 8. If the items we’re removed using the pop operation, they would be returned in the reverse of the order they were put it, 5, then 10, and finally 8.

Stacks Stacks are used in a wide array of applications. They can be used to evaluate equations as well as keep track of function calls in a program that is running. Stacks are used in a wide array of applications. They can be used to evaluate equations as well as keep track of function calls in a program that is running.