Stacks and Queues Processing Sequences of Elements Soft

Stacks and Queues Processing Sequences of Elements Soft. Uni Team Technical Trainers Software University http: //softuni. bg Advanc ed C#

Table of Contents 1. Stack<T> (LIFO – last in, first out) § Push(), Pop(), Peek(), To. Array(), Contains() and Count 2. Queue<T> (FIFO – first in, first out) § Enqueue(), Dequeue(), Peek(), To. Array(), Contains() and Count 2

Questions sli. do #CSharp-Advanced 3

2 10 5 Stack<T> Overview

Stack – Abstract Data Type § Stacks provide the following functionality: § Pushing an element at the top of the stack § Popping element from the top fo the stack § Getting the topmost element without removing it 10 10 10 5 5 5 2 2 2 Push Pop Peek 5

Push() – Adds an element on top of the Stack 10 52 Stack<int> Count: 2 0 3 1 6

Pop() – Returns the last element from the stack and removes it Stack<int> 2 Count: 2 1 3 10 5 7

Peek() – Returns the last element from the stack without removing it Stack<int> Count: 1 5 8

Problem: Reversing Strings § Create a program that: § Reads an input string § Reverses it using a Stack Input Output I Love C# #C evo. L I Stacks and Queues seueu. Q dna skcat. S Check your solution here: https: //judge. softuni. bg/Contests/ 9

Solution: Reversing Strings var input = Console. Read. Line(); var stack = new Stack<char>(); foreach (var ch in input) { stack. Push(ch); } while (stack. Count != 0) { Console. Write(stack. Pop()); } Console. Write. Line(); Count property is used without parentheses Check your solution here: https: //judge. softuni. bg/Contests/Practice/Index/386#0 10

Stack – Constructors Stack<int> stack = new Stack<int>(); Stack<int> stack = new Stack<int>(12); Specified initial capacity of internal array string[] values = { “Advanced", “OOP Advanced" }; Stack<string> stack = new Stack<string>(values); Copied elements from the specified collection and remains their order 11

Stack – Utility Methods Stack<int> stack = new Stack<int>(); int count = stack. Count; bool exists = stack. Contains(2); int[] array = stack. To. Array(); stack. Clear(); stack. Trim. Excess(); Retains order of elements Remove all elements Resize the internal array 12

Stack<T> – Overview of all operations 132 10 15 -7 52 Stack<int> Push() Pop() 5 Count: 2 1 0 3 5 4 Peek() 13

Problem: Simple Calculator § Implement a simple calculator that can evaluate simple expressions (only addition and subtraction) Input Output 2 + 5 + 10 - 2 - 1 14 2 - 2 + 5 5 Check your solution here: https: //judge. softuni. bg/Contests/Practice/Index/386#0 14

Solution: Simple Calculator var input = Console. Read. Line(); var values = input. Split(' '); var stack = new Stack<string>(values. Reverse()); while (stack. Count > 1) { int first = int. Parse(stack. Pop()); String op = stack. Pop(); int second = int. Parse(stack. Pop()); //TODO: Add switch for operation (look next slide) } Console. Write. Line(stack. Pop()); Check your solution here: https: //judge. softuni. bg/Contests/Practice/Index/386#0 15

Solution: Simple Calculator (2) switch (op) { case "+": stack. Push((first + second). To. String()); break; case "-": stack. Push((first - second). To. String()); break; } Check your solution here: https: //judge. softuni. bg/Contests/Practice/Index/386#0 16

Problem: Decimal To Binary Converter § Create a converter which takes a decimal number and converts it into a binary number. Input Output 10 1024 100000 Check your solution here: https: //judge. softuni. bg/Contests/Practice/Index/386#0 17

Solution: Decimal To Binary Converter var decimal. Number = int. Parse(Console. Read. Line ()); var stack = new Stack<int>(); //TODO: Check if number is zero while (decimal. Number != 0) { stack. Push(decimal. Number % 2); decimal. Number /= 2; } while (stack. Count != 0) { Console. Write(stack. Pop()); } Console. Write. Line(); Check your solution here: https: //judge. softuni. bg/Contests/Practice/Index/386#0 18

Problem: Matching Brackets § We are given an arithmetical expression with brackets (with nesting) § Goal: extract all sub-expressions in brackets 1 + (2 - (2 + 3) * 4 / (3 + 1)) * 5 (2 + 3) (3 + 1) (2 - (2 + 3) * 4 / (3 + 1)) Check your solution here: https: //judge. softuni. bg/Contests/Practice/Index/386#0

Problem: Matching Brackets //TODO: Read input from console for (int i = 0; i < input. Length; i++) { char ch = input[i]; if (ch == '(') stack. Push(i); else if (ch == ')') int start. Index = stack. Pop(); string contents = input. Substring (start. Index, i – start. Index + 1); Console. Write. Line(contents); } Check your solution here: https: //judge. softuni. bg/Contests/Practice/Index/386#0

Working with Stacks Exercises in class

2 10 5 Queue<T> Overview

Queue – Abstract Data Type § Queues provide the following functionality: § Adding an element at the end of the queue 10 5 2 § Removing the first element from the queue 10 5 2 § Getting the first element of the queue without removing it 10 5 2 23

Enqueue() – Adds an element to the front of the queue Queue<int> Count: 43 2 0 1 121 15 -3 5 24

Dequeue() – Returns the first element from the queue and removes it Count: Queue<int> 121 15 -3 42 3 5 25

Peek() – Returns the first element from the queue without removing it Count: Queue<int> 121 2 15 26

Problem: Hot Potato § Children form a circle and pass a hot potato clockwise § Every nth toss a child is removed until only one remains § Upon removal the potato is passed forward § Print the child that remains last Input Output Mimi Pepi Toshko 2 Removed Pepi Removed Mimi Last is Toshko Check your solution here: https: //judge. softuni. bg/Contests/Practice/Index/386#0 27

Solution: Hot Potato var children = Console. Read. Line(). Split(' '); var number = int. Parse(Console. Read. Line()); Queue<string> queue = new Queue<string>(children); while (queue. Count != 1) Copied elements from the { specified collection and for (int i = 1; i < number; i++) remains their order { queue. Enqueue(queue. Dequeue()); } Console. Write. Line($"Removed {queue. Dequeue()}"); } Console. Write. Line($"Last in {queue. Dequeue()}"); Check your solution here: https: //judge. softuni. bg/Contests/Practice/Index/386#0 28

Queue – Utility Methods Queue<int> queue = new Queue<int>(); int count = queue. Count; bool exists = queue. Contains(2); int[] array = queue. To. Array(); queue. Clear(); queue. Trim. Excess(); Retains order of elements Remove all elements Resize the internal array 29

Queue<T> – Overview of all operations Count: Queue<int> 121 15 -3 5 4 2 1 0 3 5 Enqueue() Peek() Dequeue() 30

Problem: Math Potato § Rework the previous problem so that a child is removed only on a prime cycle (cycles start from 1) § If a cycle is prime, just print the child's name Input Output Mimi Pepi Toshko 2 Removed Pepi Prime Mimi Prime Toshko Removed Mimi Last is Toshko Check your solution here: https: //judge. softuni. bg/Contests/Practice/Index/386#0 31

Solution: Math Potato //TODO: Read input from console int cycle = 1; while (queue. Count != 1) { for (int i = 1; i < number; i++) { queue. Enqueue(queue. Dequeue()); } //TODO: Check if cycle is Prime, look at next slide cycle++; } Console. Write. Line($"Last in {queue. Dequeue()}"); Check your solution here: https: //judge. softuni. bg/Contests/Practice/Index/386#0 32

Solution: Math Potato (2) You need to write your own tool for checking if numbers is prime if (Prime. Tool. Is. Prime(cycle)) { Console. Write. Line($"Prime {queue. Peek()}"); } else { Console. Write. Line($"Removed {queue. Dequeue()}"); } Check your solution here: https: //judge. softuni. bg/Contests/Practice/Index/386#0 33

Working with Queues Exercises in class

Summary § Stack<T> § LIFO data structure § Queue<T> § FIFO data structure 35

Stacks and Queues ? s n stio e u Q ? ? ? https: //softuni. bg/courses/advanced-csharp

License § This course (slides, examples, demos, videos, homework, etc. ) is licensed under the "Creative Commons Attribution. Non. Commercial-Share. Alike 4. 0 International" license § Attribution: this work may contain portions from § "Fundamentals of Computer Programming with C#" book by Svetlin Nakov & Co. under CC-BY-SA license § "C# Part I" course by Telerik Academy under CC-BY-NC-SA license § "C# Part II" course by Telerik Academy under CC-BY-NC-SA license 37

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