HashSet for unique elements in C Sharp (C#) - Step-by-Step Execution

Concept Flow - HashSet for unique elements

Create empty HashSet

↓

Add element?

No→Skip add

Yes↓

Element added if unique

↓

More elements?

No→End

↩Back to Add element?

Start with an empty HashSet, try to add elements one by one. Only unique elements get added. Repeat until no more elements.

Execution Sample

C Sharp (C#)

var set = new HashSet<int>();
set.Add(1);
set.Add(2);
set.Add(1);
Console.WriteLine(set.Count);

Adds numbers to a HashSet and prints how many unique numbers are inside.

Execution Table

Step	Action	Element Added	Set Contents	Output
1	Create empty HashSet	N/A	{}
2	Add 1	1	{1}
3	Add 2	2	{1, 2}
4	Add 1 again	No (duplicate)	{1, 2}
5	Print Count	N/A	{1, 2}	2

💡 All elements processed; duplicates ignored; final count is 2

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	Final
set	{}	{1}	{1, 2}	{1, 2}	{1, 2}

Key Moments - 2 Insights

Why doesn't adding '1' the second time change the set?

Because HashSet only keeps unique elements. Step 4 in the execution_table shows 'Add 1 again' is ignored since '1' is already inside.

What does set.Count represent?

It shows how many unique elements are in the set. Step 5 prints '2' because only two unique numbers (1 and 2) were added.

Visual Quiz - 3 Questions

Look at the execution_table, what is the set content after step 3?

A {}

B {1, 2}

C {1}

D {2}

💡 Hint

Check the 'Set Contents' column at step 3 in the execution_table.

At which step is a duplicate element detected and not added?

A Step 4

B Step 2

C Step 3

D Step 5

💡 Hint

Look for 'No (duplicate)' in the 'Element Added' column in the execution_table.

If we add '3' after step 4, what will be the new count?

A 4

B 2

C 3

D 1

💡 Hint

Adding a new unique element increases the count by 1; see variable_tracker for how set changes.

Concept Snapshot

HashSet stores unique elements only.
Use Add() to insert elements; duplicates are ignored.
Count property shows number of unique items.
Ideal for removing duplicates quickly.

Full Transcript

This example shows how a HashSet in C# keeps only unique elements. We start with an empty set. Adding '1' puts it inside. Adding '2' adds another unique element. Trying to add '1' again does nothing because it's a duplicate. Finally, printing Count shows 2, the number of unique elements. HashSet is useful when you want to avoid duplicates automatically.