data structures leon andretti abdillah · a stack is a data structure that allows data to be...

05

Stack

(Tumpukan)

Data Structures

Leon Andretti Abdillah

Introduction 1/4

A stack is a list of homogenous elements in which the

addition and deletion of elements occurs only at one end,

called the top of the stack.

A stack is a data structure of ordered items such that items can be

inserted and removed only at one end.

10/04/2013 18:34:362 LeonAbdillah - DS - Stack

Introduction 2/4

10/04/2013 18:34:36LeonAbdillah - DS - Stack3

A stack is a data structure that allows data to be inserted (a

'push' operation), and removed (a 'pop' operation). Many

stacks also support a read ahead (a 'peek' operation), which

reads data without removing it. A stack is a LIFO-queue,

meaning that the last data to be inserted will be the first data

to be removed.

When we insert data into a stack, it is placed at the head of a

queue. This means that when we remove data, it will be in

reverse order. Adding 1,2,3,4 will return 4,3,2,1. Stacks

aren't the most frequently used data structure, but they are

extremely useful for certain tasks.

Introduction 3/4


For example, in a cafeteria, the second tray in a stack of trays can be removed only if the first tray has been removed.

For another example, to get to your favorite computer science book, which is underneath your math and history books, you must first remove the math and history books. After removing these books, the computer science book becomes the top book—that is, the top element of the stack.

The simplest application of a stack is to reverse a word. You push a given word to stack - letter by letter - and then pop letters from the stack.

Another application is an "undo" mechanism in text editors; this operation is accomplished by keeping all text changes in a stack.

Introduction 4/4

Various examples of stack


Stack ADT (Abstract Data Structure)

6

stack: a list with the restriction that insertions/deletions can only be performed at the top/end of the list Last-In, First-Out ("LIFO") The elements are stored in order of insertion,

but we do not think of them as having indexes. The client can only add/remove/examine

the last element added (the "top").

basic stack operations: push: Add an element to the top. pop: Remove the top element. peek: Examine the top element.

10/04/2013 18:34:37LeonAbdillah - DS - Stack

Stack only defines the default constructor, which creates an empty stack.

To put an object on the top of the stack, call push( ). To remove and return the top element, call pop( ). An EmptyStackException is thrown if you call pop( )when the invoking stack is empty. You can use peek( ) to return, but not remove, the top object.

The empty() method returns true if nothing is on the stack. The search() method determines whether an object exists on the stack, and returns the number of pops that are required to bring it to the top of the stack.


Stack’s methods/operations

A Stack adds and removes elements on a First-In First-Out

basis.The key methods of the Stack class are push(), peek(),

pop(), empty() and search().

Operations Notes

push() adds an element to the top of the stack.

peek() returns the first element from the top of the stack without

removing it from the stack.

pop() as peek() but removes it from the stack.

empty() checks wheater there are elements in the stack or not.

search() returns the position of an element in the stack


Java for stack


Java provides a stack implementation, in the form of

java.util.Stack. Stack's are a subclass of

java.util.Vector, and share some similarities. A

Vector, after all, is a queue, and a Stack is an ordered LIFO

queue.

Stacks are quite easy to use.

Here's a sample application that uses a stack of numbers.

Java Example 1/9


Pada java project yg sdh ada (StrukturData)

Create new Package (;package04)

Pada package yg baru tercipta, create new class

(;StackDemo)

Java Example 2/9a


package package04;

public class StackDemo {

/**

* @param args

*/

public static void main(String[] args) {

// TODO Auto-generated method stub

}

}

Java Example 2/9b


package package04;

// add two libraries after package and before ClassName

import java.util.EmptyStackException;

import java.util.Stack;

public class StackDemo {

/**

* @param args

*/



}

}

Java Example 3/9


Define a method showpush before main()

static void showpush(Stack st, int a) {

st.push(new Integer(a));

System.out.println("push(" + a + ")");

System.out.println("stack: " + st);

}

Java Example 4/9


Define a method showpop before main()

static void showpop(Stack st) {

System.out.print("pop -> ");

Integer a = (Integer) st.pop();

System.out.println(a);


}

Java Example 5/5


Define a method showpeek before main()

static void showpeek(Stack st) {

System.out.print("peek -> ");

Integer a = (Integer) st.peek();

System.out.println(a);


}

Java Example 6/9


Define a method showpeek before main()

static void showsearch(Stack st, int b) {

int pos = st.search(b);

System.out.println("Location of " + b + " is : " + pos);

}

Java Example 7/9


Add statements in main()



Stack st = new Stack(); // create Stack


showpush(st, 42);

showpush(st, 66);

showpush(st, 99);

System.out.println("stack size: " + st.size());

Java Example 8/9


showsearch(st, 42);

showsearch(st, 66);

showsearch(st, 99);

showpeek(st);

showpop(st);

showpop(st);

showpop(st);

Java Example 9/9


try {

showpop(st);

} catch (EmptyStackException e) {

System.out.println("empty stack");

}

// Or

System.out.println("Is the stack empty? "+ st.empty());

} // main()

} // class

Result


Summary

Stack:

LIFO

Operations

push

pop

top /peek

search

Applications (Homework)

Depth-first search

Recursive evaluation


data structures leon andretti abdillah · a stack is a data structure that allows data to be...

Documents