Set
Domain: Data Structures
🎯 Motivation
When you need to track unique items and check membership instantly — deduplication, tags, visited nodes — a set is the right structure.
📋 Concrete Example
visited = set(); visited.add('nodeA'); 'nodeA' in visited returns True. Adding nodeA again does nothing — duplicates are ignored.
🔗 Analogy
A stamp collection. You only keep one of each stamp design. If someone gives you a duplicate, it bounces out. Checking if you have a stamp is a quick glance.