HashSet for unique elements in C Sharp (C#) - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a HashSet in C#?

A HashSet is a collection that stores unique elements only. It does not allow duplicates and provides fast lookup, add, and remove operations.

beginner

How does a HashSet ensure elements are unique?

HashSet uses a hash function to quickly check if an element already exists before adding it. If the element is already present, it won't add it again.

beginner

Which method is used to add an element to a HashSet in C#?

The Add() method is used to add an element. It returns true if the element was added, or false if it was already present.

beginner

What happens if you try to add a duplicate element to a HashSet?

The HashSet ignores the duplicate and does not add it again. The Add() method returns false to indicate the element was not added.

beginner

How can you check if a HashSet contains a specific element?

Use the Contains() method. It returns true if the element is in the HashSet, otherwise false.

What does a HashSet in C# store?

A Only unique elements

B Elements in sorted order

C Key-value pairs

D Duplicates allowed

A HashSet stores only unique elements and does not allow duplicates.

Which method adds an element to a HashSet?

A Insert()

B Push()

C Append()

D Add()

The Add() method is used to add elements to a HashSet.

What does Add() return if you add a duplicate element to a HashSet?

A false

B throws an error

C null

D true

Add() returns false if the element is already in the HashSet and not added again.

How can you check if a HashSet contains an element?

A Find()

B Exists()

C Contains()

D Search()

Contains() checks if an element is present in the HashSet.

Which of these is NOT a feature of HashSet?

A Stores unique elements

B Allows duplicates

C Fast lookup

D No guaranteed order

HashSet does NOT allow duplicates; it only stores unique elements.

Explain what a HashSet is and why it is useful for storing unique elements.

Think about how you keep a list of friends without repeats.

Describe how you would add elements to a HashSet and check if an element exists.

Adding is like putting a name on a guest list; checking is like asking if a name is already there.