ADT vs Physical Data Structure — TechAmbitionX | DSA
1. What is an ADT (Abstract Data Type)?
Definition: An ADT tells you what operations you can perform, not how they’re done.
Analogy: Think of it as a menu in a restaurant. The menu says you can order “Pizza, Burger, Pasta” — but it doesn’t tell you how the chef cooks them.
Examples:
- Stack (push, pop, peek)
- Queue (enqueue, dequeue)
- List (insert, delete, traverse)
So, ADTs = concept + behavior.
🔹 2. What is a Physical Data Structure?
Definition: This is the real recipe and ingredients in the kitchen that actually make the food.
Analogy: If ADT is the menu → the Physical Structure is the kitchen setup (utensils, oven, storage).
Examples:
- Array (continuous memory)
- Linked List (nodes + pointers)
- Tree (nodes with parent-child links)
- Graph (nodes + edges)
- Hash Table (key-value pairs with hashing function)
So, Physical Structures = implementation + memory layout.
🔹 3. Relationship Between the Two
ADT is the idea / contract — Physical Structure is the implementation.
👉 One ADT can be implemented using different physical structures.
Example — Stack (ADT):
- Array → fixed size (or dynamic), direct indexing.
- Linked List → dynamic size, extra pointer overhead for links.
👉 The choice depends on what trade-offs you want: speed, memory, or flexibility.
🔹 4. Real-Life Analogy
ADT = Blueprint of a house (what rooms it should have, how many floors).
Physical Structure = Actual construction (bricks, wood, cement).
Different builders (structures) can realize the same blueprint (ADT).
🔹 5. Quick Example Table
| ADT | Possible Physical Structures |
|---|---|
| Stack | Array, Linked List |
| Queue | Array, Linked List, Circular Array |
| Map | Hash Table, Balanced Tree |
| List | Array, Linked List |
Quick recap
ADT = what you can do (contract). Physical structure = how it’s stored (implementation). Pick your implementation based on trade-offs: speed, memory, simplicity.
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