Lesson 3 - Stack ADT.pdf
- 1. STACK ADT Jun Y. Ercia
- 2. The Stack ADT Objectives • examine stack processing • define a stack abstract data type • demonstrate how a stack can be used to solve problems • examine various stack implementations • compare stack implementations
- 3. The Stack ADT Data a collection whose elements are added and removed from one end, called the top of the stack. a stack is a Last In, First Out (LIFO) data structure Example • Stack of plates in a cafeteria Note ▪ items are removed from a stack in the reverse order from the way they were inserted ▪ It is not legal to access any item other than the one that is at the top of the stack!
- 4. Operations on a Stack
- 5. Stack Errors 1. Underflow – occurs when trying to pop (or peek at) an empty stack 2. Overflow – occurs when trying to push onto an already full stack
- 6. Uses of Stacks in Computing Stack is useful for any kind of problem involving LIFO data 1. Calculators: − Convert infix expressions to postfix to make evaluation easier − Evaluate postfix expressions 2. Compilers: − to convert infix expressions to postfix, to make translation to lower level language easier 3. Word processors, editors, etc: − to check expressions or strings of text for matching parentheses − to implement undo operations ▪ keeps track of the most recent operations ▪ why are they kept in reverse order?
- 7. Implementation of Stack ADT 1. Array implementation of Stack ▪ The entire stack is represented by an array together with a pointer top pointing to the next available cell in the array. ▪ An empty stack is represented with top pointing to the first cell in the array. ▪ Suitable for applications in which the maximum stack size is known ahead of time.
- 8. Code for adding an item to the top of the stack
- 9. Code for removing the item most recently added
- 10. Code for determining whether the stack is empty
- 11. Code for determining whether the stack is full
- 12. Code for making the stack empty
- 13. Code for retrieving the item most recently added
- 14. Implementation of Stack ADT 1. Linked List implementation of Stack ▪ The entire stack is represented by a linked list of nodes together with a pointer top pointing to the first node of the linked list. ▪ An empty stack is represented with top pointing NULL. ▪ Suitable for applications in which the maximum stack size is not known beforehand. Note ▪ With a linked-list representation, overflow will not happen (unless you exhaust memory, which is another kind of problem) ▪ Underflow can happen, and should be handled.
- 15. Code for adding an item to the top of the stack
- 16. Code for removing the item most recently added
- 17. Code for determining whether the stack is empty
- 18. Code for making the stack empty
- 19. Code for retrieving the item most recently added