Lære Introduction to Sets | Sets and Collection Utilities

A set is a collection type that stores unique elements only—no duplicates are allowed. In C#, the most common implementation is HashSet<T>, where T is the type of elements you want to store. This makes sets especially useful when you need to eliminate duplicates or quickly check if an item already exists.

To use a HashSet<T>, you declare it by specifying the type of elements in angle brackets. For example, to store integers, you write HashSet<int>. You can add elements using the Add method, and if you try to add a duplicate, the set will simply ignore it. This built-in duplicate prevention is what makes sets different from lists or arrays, which allow repeated values.

Program.cs


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using System;
using System.Collections.Generic;

namespace ConsoleApp
{
    public class Program
    {
        public static void Main(string[] args)
        {
            HashSet<int> numbers = new HashSet<int>();

            numbers.Add(10);
            numbers.Add(20);
            numbers.Add(30);
            numbers.Add(10); // Duplicate, will be ignored

            Console.WriteLine("Numbers in the set:");
            foreach (int number in numbers)
            {
                Console.WriteLine(number);
            }
        }
    }
}

When you add elements to a HashSet<T>, each value is checked for uniqueness. If the value already exists, it is not added again. To check if a value exists, use the Contains method. To remove a value, use the Remove method. Here is a step-by-step breakdown:

Create a new HashSet<T> by specifying the type in angle brackets;
Add elements using the Add method;
Use Contains to check if an element is present;
Remove elements with the Remove method.

This workflow allows you to manage a collection of unique items efficiently.

Program.cs


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using System;
using System.Collections.Generic;

namespace ConsoleApp
{
    public class Program
    {
        public static void Main(string[] args)
        {
            HashSet<int> setA = new HashSet<int> { 1, 2, 3, 4 };
            HashSet<int> setB = new HashSet<int> { 3, 4, 5, 6 };

            setA.UnionWith(setB);
            Console.WriteLine("After UnionWith, setA contains:");
            foreach (int n in setA)
            {
                Console.WriteLine(n);
            }

            setA = new HashSet<int> { 1, 2, 3, 4 };
            setA.IntersectWith(setB);
            Console.WriteLine("After IntersectWith, setA contains:");
            foreach (int n in setA)
            {
                Console.WriteLine(n);
            }
        }
    }
}

1. What is the main feature of a HashSet?

2. Which method checks if a value exists in a HashSet?

3. Fill in the blanks to add elements to a `HashSet<string>`.

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Sektion 3. Kapitel 1

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Suggested prompts:

Can you give an example of how to use HashSet in C#?

What are some real-world scenarios where HashSet is useful?

How does HashSet compare to other collection types like List or Dictionary?

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Program.cs


              12345678910111213141516171819202122232425
            
using System;
using System.Collections.Generic;

namespace ConsoleApp
{
    public class Program
    {
        public static void Main(string[] args)
        {
            HashSet<int> numbers = new HashSet<int>();

            numbers.Add(10);
            numbers.Add(20);
            numbers.Add(30);
            numbers.Add(10); // Duplicate, will be ignored

            Console.WriteLine("Numbers in the set:");
            foreach (int number in numbers)
            {
                Console.WriteLine(number);
            }
        }
    }
}

Create a new HashSet<T> by specifying the type in angle brackets;
Add elements using the Add method;
Use Contains to check if an element is present;
Remove elements with the Remove method.

This workflow allows you to manage a collection of unique items efficiently.

Program.cs


              123456789101112131415161718192021222324252627282930
            
using System;
using System.Collections.Generic;

namespace ConsoleApp
{
    public class Program
    {
        public static void Main(string[] args)
        {
            HashSet<int> setA = new HashSet<int> { 1, 2, 3, 4 };
            HashSet<int> setB = new HashSet<int> { 3, 4, 5, 6 };

            setA.UnionWith(setB);
            Console.WriteLine("After UnionWith, setA contains:");
            foreach (int n in setA)
            {
                Console.WriteLine(n);
            }

            setA = new HashSet<int> { 1, 2, 3, 4 };
            setA.IntersectWith(setB);
            Console.WriteLine("After IntersectWith, setA contains:");
            foreach (int n in setA)
            {
                Console.WriteLine(n);
            }
        }
    }
}

1. What is the main feature of a HashSet?

2. Which method checks if a value exists in a HashSet?

3. Fill in the blanks to add elements to a `HashSet<string>`.

Var alt klart?

Tak for dine kommentarer!

Sektion 3. Kapitel 1

Introduction to Sets

1. What is the main feature of a HashSet?

2. Which method checks if a value exists in a HashSet?

3. Fill in the blanks to add elements to a HashSet<string>.

Introduction to Sets

1. What is the main feature of a HashSet?

2. Which method checks if a value exists in a HashSet?

3. Fill in the blanks to add elements to a HashSet<string>.

3. Fill in the blanks to add elements to a `HashSet<string>`.

3. Fill in the blanks to add elements to a `HashSet<string>`.