Transcript Stack

ANNOUNCEMENTS
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HW-6 Deadline Extended to April
27th
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Final Exam – May 2nd at 7-9 PM in
Olsson Hall Room 120
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Exam will be 33% longer than Exams 1 and 2
33% of the material are from those
covered in Exams 1 and 2
In-Class final exam review session - April
20th
Make-up exam slots and criteria will be
announced via e-mail. Sign-up for the makeup exam slot that works for you.
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Data Structures
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Data Structures
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Arrays
Fixed size
Lists
A collection of a variable number of items
Typical Operations on Lists
Add an item to the list
Remove an item from the list
Read an item from the list
Check whether the list is empty
Get the current size of the list
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Lists Can Be Organized in Different Ways
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Linked List
Linear sequence of elements
Queue
Remove the item least recently added.
First-In, First-Out (FIFO)
Stack
Remove the item most recently added.
Last-In, First-Out (LIFO)
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Generics
Generics. Parameterize the datatype used in the data
structure.
You need to import the library: import java.util.ArrayList;
ArrayList<Apple> list= new ArrayList<Apple>();
Apple a = new Apple();
Orange b = new Orange();
list.add(a);
list.add(b);
// compile-time error
a = list.get(0); // returns an Apple object
sample client
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Autoboxing
Generic ArrayList implementation. Only permits reference types.
Wrapper type.
Each primitive type has a wrapper reference type.
Ex: Integer is wrapper type for int.
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Autoboxing. Automatic cast from primitive type to wrapper type.
Autounboxing. Automatic cast from wrapper type to primitive type.
ArrayList<Integer> list= new ArrayList<Integer>();
list.add(17);
// autobox
(int -> Integer)
int a = list.get(i);
// autounbox (Integer -> int)
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Queues
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Queue API
Iterator<Key>
return an iterator over the keys
iterator()
enqueue
dequeue
length
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Array Implementation of Queues
With an array q[].
Head (Keep track of the front of the queue)
Tail (Keep track of the back of the queue)
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head
tail
enQueue(Item) {
Add item after the last element of the array;
}
Item deQueue(Item) {
Remove and return the first element in the array;
}
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Arraylist Implementation (Coding Demo)
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How Do We Implement a Circular Queue?
Add elements 1 … n
st element overwrites the 1st element
The (n+1)
Update head and tail modulo the capacity (n).
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Stacks
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Stack
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Last-In, First-Out (LIFO) List
Items are added to the top of the stack
(push)
Items are removed from the top of the
stack (pop)
push
pop
Top of Stack
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Stack Applications
Real world applications.
Parsing in a compiler.
Undo in a word processor.
Back button in a Web browser.
Implementing function calls in a compiler.
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Stack API
Stack<Item> Stack; //create an empty stack
boolean IsEmpty(); //check whether the stack is empty
void push(Item); //push an item onto the stack
Item pop(); //pop the stack
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Stack: Array Implementation
Array implementation of a stack.
Use array a[] to store N items on stack.
Use the last index of the array to keep track of the stack top
push() add new item at a[N].
pop() remove item from a[N-1].
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a[]
it
was
the
best
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Arraylist Implementation (Coding Demo)
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Summary
Stacks and queues are fundamental ADTs.
Array implementation.
Linked list implementation.
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Many applications.
NEXT CLASS: Review for Final Exam
NO CLASS on April 22nd and 27th but will hold office-hours during
those times in Olsson 236B
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