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HashSet vs TreeSet 🚀

Mentor's Note: A Set is your best friend when you want to make sure there are NO duplicates in your data. It's like a high-security ID scanner! 💡

🌟 The Scenarios: The Pile 🧺 vs. The Library Shelf 📚

  • HashSet (The Laundry Pile): You throw all your unique shirts into one big pile. You don't care about the order, you just want to reach in and grab one specific shirt instantly. 📦
  • TreeSet (The Library Shelf): You arrange every book in perfect alphabetical order. It takes longer to put a book on the shelf, but the library is always Sorted. 📦
  • The Result: HashSet is the fastest for searching, while TreeSet is the best for ordered data. ✅

📖 Key Differences

1. Java HashSet

  • Logic: Uses a Hash Table.
  • Order: No guaranteed order (Random appearance).
  • Performance: \(O(1)\) (Constant time search). ⚡

2. Java TreeSet

  • Logic: Uses a Red-Black Tree.
  • Order: Always sorted (Ascending by default).
  • Performance: \(O(\log n)\) (Slightly slower than HashSet).

🎨 Visual Logic: Set Types

graph TD
    A[Set: No Duplicates 🛡️] --> B[HashSet: Random & Fast ⚡]
    A --> C[TreeSet: Sorted 📈]
    A --> D[LinkedHashSet: Insertion Order 📍]

💻 Implementation: The Set Lab

import java.util.HashSet;

// 🛒 Scenario: Tracking unique visitors
HashSet<String> visitors = new HashSet<>();
visitors.add("Vishnu");
visitors.add("Ankit");
visitors.add("Vishnu"); // ❌ Duplicate rejected

System.out.println(visitors.size()); // Result: 2

import java.util.TreeSet;

// 🛒 Scenario: A High Score Board
TreeSet<Integer> scores = new TreeSet<>();
scores.add(50);
scores.add(100);
scores.add(10);

// 🛍️ Outcome: Always printed as [10, 50, 100]
System.out.println(scores);

📊 Sample Dry Run (HashSet)

Table capacity: 8 buckets

| Action | Logic | Hash Bucket | | :--- | :--- | :--- | :--- | | add("A") | Hash("A") = 3 | Item goes to Bucket 3 📥 | | add("B") | Hash("B") = 5 | Item goes to Bucket 5 📥 | | add("A") | Already in 3 | REJECTED ❌ |

📉 Technical Analysis

  • Null Values: HashSet allows one null value. TreeSet does not allow null because it can't compare null to other values for sorting! ⚠️

🎯 Practice Lab 🧪

Task: The Duplicate Remover

Task: You have a list of names with duplicates: ["John", "Ankit", "John", "Sara"]. Use a HashSet to extract only the unique names and print them. Hint: new HashSet<>(myList). 💡

💡 Interview Tip 👔

"Interviewers love this: 'How does a Set know if an item is a duplicate?' Answer: It uses the hashCode() and equals() methods of the object to check for a match!"

💡 Pro Tip: "One interface, multiple implementations—that's the power of being flexible!" - Anonymous

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