Dictionary and Sets

🗃️ C# Collections: Your Magical Storage Boxes

Imagine you have different types of boxes to organize your toys. Each box has special powers!

🎭 The Story of Four Amazing Containers

Once upon a time, there were four magical containers in the land of C#. Each one had a special superpower for storing things. Let’s meet them!

📖 Dictionary: The Label Maker

What Is It?

A Dictionary is like a box where every toy has a name tag attached to it.

Think of it like: Your school cubby! Each cubby has a student’s name, and inside is that student’s stuff. You say “Give me Sarah’s backpack” and boom—you get it instantly!

// Creating your cubby system
Dictionary<string, string> cubbies =
    new Dictionary<string, string>();

// Adding items to cubbies
cubbies["Sarah"] = "Blue backpack";
cubbies["Tom"] = "Red lunchbox";
cubbies["Mia"] = "Purple jacket";

// Getting Sarah's item
string item = cubbies["Sarah"];
// Result: "Blue backpack"

Why Is Dictionary Special?

Real-Life Examples

// Phone contacts
Dictionary<string, string> contacts =
    new Dictionary<string, string>();
contacts["Mom"] = "555-1234";
contacts["Dad"] = "555-5678";

// Game scores
Dictionary<string, int> scores =
    new Dictionary<string, int>();
scores["Player1"] = 100;
scores["Player2"] = 85;

Key Dictionary Methods

// Check if a key exists
if (cubbies.ContainsKey("Sarah"))
{
    Console.WriteLine("Sarah has a cubby!");
}

// Safe way to get values
if (cubbies.TryGetValue("Tom", out string stuff))
{
    Console.WriteLine(quot;Tom has: {stuff}");
}

// Remove an item
cubbies.Remove("Mia");

// Count items
int total = cubbies.Count;

🌟 Golden Rule: Every key must be unique! You can’t have two “Sarah” cubbies.

🎯 HashSet: The “No Copies Allowed” Club

What Is It?

A HashSet is like a special club where no duplicates are allowed. If you try to add something twice, it just ignores the second one!

Think of it like: A birthday party guest list. Each person can only be on the list once—writing “Emma” twice doesn’t invite two Emmas!

// Creating a guest list
HashSet<string> guestList = new HashSet<string>();

// Adding guests
guestList.Add("Emma");
guestList.Add("Liam");
guestList.Add("Emma"); // Ignored! Emma's already there

Console.WriteLine(guestList.Count);
// Result: 2 (not 3!)

Why Use HashSet?

graph TD
    A["Add Item"] --> B{Already exists?}
    B -->|Yes| C["Ignore it"]
    B -->|No| D["Add to set"]
    C --> E["Set unchanged"]
    D --> E

Cool HashSet Tricks

HashSet<int> myNumbers = new HashSet<int>
    { 1, 2, 3, 4, 5 };
HashSet<int> yourNumbers = new HashSet<int>
    { 4, 5, 6, 7, 8 };

// Numbers we BOTH have
myNumbers.IntersectWith(yourNumbers);
// Result: { 4, 5 }

// Combine all unique numbers
HashSet<int> all = new HashSet<int>
    { 1, 2, 3, 4, 5 };
all.UnionWith(new HashSet<int> { 4, 5, 6, 7, 8 });
// Result: { 1, 2, 3, 4, 5, 6, 7, 8 }

When to Use HashSet?

• ✅ Removing duplicates from a list
• ✅ Checking if something exists (super fast!)
• ✅ Finding common items between groups
• ✅ Tracking “already seen” items

📚 Queue: The Fair Line

What Is It?

A Queue is like a line at the ice cream shop. First person in line gets served first!

Think of it like: Waiting for a slide at the playground. The kid who got in line first goes down the slide first. No cutting!

// Kids waiting for the slide
Queue<string> slideLine = new Queue<string>();

// Kids join the line
slideLine.Enqueue("Alex");   // First in line
slideLine.Enqueue("Beth");   // Second
slideLine.Enqueue("Carlos"); // Third

// Who goes down the slide?
string firstKid = slideLine.Dequeue();
// Result: "Alex" goes first!

// Who's next?
string nextKid = slideLine.Peek();
// Result: "Beth" (but she stays in line)

Queue Flow

graph LR
    A["New Person"] -->|Enqueue| B["Back of Line"]
    B --> C["Middle"]
    C --> D["Front of Line"]
    D -->|Dequeue| E["Gets Served!"]

Queue Keywords

Real Examples

// Print jobs waiting
Queue<string> printJobs = new Queue<string>();
printJobs.Enqueue("Report.pdf");
printJobs.Enqueue("Photo.jpg");
printJobs.Enqueue("Letter.doc");

// Process jobs in order
while (printJobs.Count > 0)
{
    string job = printJobs.Dequeue();
    Console.WriteLine(quot;Printing: {job}");
}

🥞 Stack: The Pancake Pile

What Is It?

A Stack is like a pile of pancakes. You can only take the top pancake!

Think of it like: A stack of books on your desk. To get the bottom book, you have to remove all the books on top first!

// Stacking pancakes
Stack<string> pancakes = new Stack<string>();

// Adding pancakes (bottom to top)
pancakes.Push("Blueberry");   // Bottom
pancakes.Push("Chocolate");   // Middle
pancakes.Push("Maple");       // Top!

// Eating pancakes (top first!)
string firstBite = pancakes.Pop();
// Result: "Maple" (the top one!)

// What's on top now?
string next = pancakes.Peek();
// Result: "Chocolate"

Stack Flow

graph TD
    subgraph Stack
        A["TOP: Maple"]
        B["Chocolate"]
        C["BOTTOM: Blueberry"]
    end
    D["Pop"] --> A
    E["Push New"] --> A

Stack Keywords

Real Examples

// Undo button in a drawing app
Stack<string> history = new Stack<string>();

// User draws things
history.Push("Drew circle");
history.Push("Drew square");
history.Push("Drew triangle");

// User clicks Undo
string undone = history.Pop();
// Undoes: "Drew triangle" (most recent!)

🎪 Quick Comparison

🧙‍♂️ Magic Memory Trick

Dictionary = Directory (look up by name) HashSet = Has it? (yes/no, no copies) Queue = Queing up fairly (first come, first served) Stack = Stacked plates (take from top)

🎯 When to Use What?

graph TD
    A["Need to store data?"] --> B{Need to find by key?}
    B -->|Yes| C["Use Dictionary"]
    B -->|No| D{Need to prevent duplicates?}
    D -->|Yes| E["Use HashSet"]
    D -->|No| F{Need fair order?}
    F -->|Yes, FIFO| G["Use Queue"]
    F -->|No, LIFO| H["Use Stack"]

🌈 Fun Summary

Remember: Each container has its superpower. Pick the right one for your mission!

Now you’re ready to organize data like a pro! Go build something amazing! 🚀