Download presentation

Presentation is loading. Please wait.

Published byAmira Danes Modified over 2 years ago

1
Lecture 5 Stack Sandy Ardianto & Erick Pranata © Sekolah Tinggi Teknik Surabaya 1

2
» In computer science, a stack is a last-in first-out (LIFO) data structure. » A stack can have any data type as an element, but is characterized by only two fundamental operations, the push and pop. © Sekolah Tinggi Teknik Surabaya 2

3
» The push operation adds to the top of the list, hiding any items already on the stack, or initializing the stack if it is empty. ˃Push is implemented by a procedure. » The pop operation removes an item from the top of the stack, and returns this value to the caller. ˃Pop is implemented by a function © Sekolah Tinggi Teknik Surabaya 3

4
» Stack was first proposed in 1955, and then patented in 1957, by the German Friedrich L. Bauer. » The same concept was developed independently, at around the same time, by the Australian Charles Leonard Hamblin. 4 © Sekolah Tinggi Teknik Surabaya

5
» In modern computer languages, the stack is usually implemented with more operations than just push and pop. » Some implementations have a function which returns the current length of the stack. » Another typical helper operation, peek, can return the current top element of the stack without removing it from the stack. 5 © Sekolah Tinggi Teknik Surabaya

6
» In most high level languages, a stack can easily implemented either through an array or a linked list. 6 © Sekolah Tinggi Teknik Surabaya

7
» The array implementation aims to create an array where the zero-offset position is the bottom. That is, array[0] is the bottom. » The program keeps track of which offset index corresponds to the top. This index changes as the stack shrinks and grows in size. 7 © Sekolah Tinggi Teknik Surabaya

8
public class STACK { const int STACK_SIZE = 1000; public int top; public int[] items(STACK_SIZE); 8 © Sekolah Tinggi Teknik Surabaya

9
public STACK() { top = -1; } 9 © Sekolah Tinggi Teknik Surabaya

10
public bool IsEmpty() { return s.top == -1; } public bool IsFull() { return s.top == STACKSIZE – 1; } 10 © Sekolah Tinggi Teknik Surabaya

11
public void Push(int x) { if (IsFull(s)) { throw new Exception("stack overflow"); } else { top = top + 1; items(top) = x; } } 11 © Sekolah Tinggi Teknik Surabaya

12
public int Pop() { if (IsEmpty()) { throw new Exception("stack underflow"); } else { int data = items(top); top = top – 1; return data; } } 12 © Sekolah Tinggi Teknik Surabaya

13
public int Pop() { if (IsEmpty()) { throw new Exception("stack underflow"); } else { int data = items(top); top = top – 1; return data; } } 13 © Sekolah Tinggi Teknik Surabaya Peek()

14
» The stack data structure ˃Elements are from the same type T ˃T can be any type, e.g. Stack ˃Size is dynamically increased as needed » Basic functionality: ˃Push(T) – inserts elements to the stack ˃Pop() – removes and returns the top element from the stack 14 © Sekolah Tinggi Teknik Surabaya

15
» Basic functionality: ˃Peek() – returns the top element of the stack without removing it ˃Count – returns the number of elements ˃Clear() – removes all elements ˃Contains(T) – determines whether given element is in the stack ˃ToArray() – converts the stack to an array ˃TrimExcess() – sets the capacity to the actual number of elements 15 © Sekolah Tinggi Teknik Surabaya

16
static void Main() { Stack stack = new Stack (); stack.Push("1. Ivan"); stack.Push("2. Nikolay"); stack.Push("3. Maria"); stack.Push("4. George"); Console.WriteLine("Top = {0}", stack.Peek()); while (stack.Count > 0) { string personName = stack.Pop(); Console.WriteLine(personName); } 16 © Sekolah Tinggi Teknik Surabaya

17
» We are given an arithmetical expression with brackets that can be nested » Goal: extract all sub-expressions in brackets » Example: ˃1 + (2 - (2+3) * 4 / (3+1)) * 5 » Result: ˃(2+3) | (3+1) | (2 - (2+3) * 4 / (3+1)) » Algorithm: ˃For each '(' push its index in a stack ˃For each ')' pop the corresponding start index 17 © Sekolah Tinggi Teknik Surabaya

18
string expression = "1 + (2 - (2+3) * 4 / (3+1)) * 5"; Stack stack = new Stack (); for (int index = 0; index < expression.Length; index++) { char ch = expression[index]; if (ch == '(') { stack.Push(index); } else if (ch == ')') { int startIndex = stack.Pop(); int length = index - startIndex + 1; string contents = expression.Substring(startIndex, length); Console.WriteLine(contents); } 18 © Sekolah Tinggi Teknik Surabaya

19
» Calculator ˃Convert an expression (infix notation) into a postfix notation. ˃Calculate a postfix expression. ˃These two processes need a stack. 19 © Sekolah Tinggi Teknik Surabaya

20
» There are three notations of expressions: infix, prefix, and postfix. Infix: 1 + 5 * 3 + 21 + (2 + 3) Prefix: + + 1 * 5 3 2+ 1 + 2 3 Postfix: 1 5 3 * + 2 +1 2 3 + + » Infix can contain parentheses, but prefix and postfix cannot (never need parentheses). 20 © Sekolah Tinggi Teknik Surabaya

21
» Push when encountering an operand. » Pop two operands and evaluate the value when encountering an operator, and then push the result. 21 © Sekolah Tinggi Teknik Surabaya

22
22

23
» Conversion from a decimal (base-10) number system to another number system ˃Examples: from decimal to binary (base-2), from decimal to octal (base-8), and from decimal to hexadecimal (base-16). ˃Suppose to convert the decimal number 156 to binary (base-2). 23 © Sekolah Tinggi Teknik Surabaya

24
» Write the integer answer (quotient) under the long division symbol, and write the remainder (0 or 1) to the right of the dividend. This remainder must be pushed into a stack. 2 ) 156 0 78 24 © Sekolah Tinggi Teknik Surabaya

25
» Continue downwards, dividing each new quotient by two and writing the remainders to the right of each dividend (pushing the remainders into a stack). Stop when the quotient is 0. 25 © Sekolah Tinggi Teknik Surabaya

26
2 ) 156 0 2 ) 78 0 2 ) 39 1 2 ) 19 1 2 ) 9 1 2 ) 4 0 2 ) 2 0 2 ) 1 1 0 26 © Sekolah Tinggi Teknik Surabaya Pop all elements from the stack to get a sequence of binary digits. 10011100

27
» Write an essay describing source code which is used to calculate infix notation. ˃Submit the printed version @ my office. ˃Due: Friday, 11 April 2014 at 5 pm. » Inappropriate essay will be returned unmarked. 27 © Sekolah Tinggi Teknik Surabaya

Similar presentations

OK

Copyright © 2001-2009 Curt Hill Stacks An Useful Abstract Data Type.

Copyright © 2001-2009 Curt Hill Stacks An Useful Abstract Data Type.

© 2017 SlidePlayer.com Inc.

All rights reserved.

Ads by Google

Ppt on non communicable diseases Ppt on management by objectives articles Ppt on inside our earth for class 7 Ppt on input and output devices of computer download Project ppt on full wave rectifier Ppt on eia of cement industry Running message display ppt on ipad Ppt on depth first search algorithm java Ppt on eia report natural gas Ppt on mindset change