Collections with no duplicates
Day 135 of 149
👉 Full deep-dive with code examples
The Guest List Analogy
You're making a party guest list:
- Add "Alice" → Alice is on the list
- Add "Bob" → Bob is on the list
- Add "Alice" again → Nothing happens! She's already there
Sets work like guest lists!
Every item appears exactly once. Duplicates are automatically ignored.
The Problem They Solve
Sometimes you need unique items:
- "What unique words are in this document?"
- "Who has visited this page?"
- "Which tags are used in this article?"
With arrays, you'd have to check for duplicates yourself. Sets handle it automatically!
What Sets Can Do
Membership check (fast!):
- "Is Alice on the list?" → Yes/No instantly
Add items:
- Adds if not there
- Ignores if already present
Remove items:
- Takes the item out
Set operations:
- Union: Combine two sets
- Intersection: What's in BOTH sets?
- Difference: What's in one but not the other?
A Simple Example
Set A: {apple, banana, cherry}
Set B: {banana, date, elderberry}
Union: {apple, banana, cherry, date, elderberry}
Intersection: {banana}
Difference (A-B): {apple, cherry}
When To Use Sets
Use sets when:
- You need unique items only
- You need fast "is this in here?" checks
- You don't care about order
- You want to find common or unique items between groups
Sets vs Arrays
| Arrays | Sets |
|---|---|
| Can have duplicates | Only unique items |
| Ordered | Usually unordered |
| Find item: slow (scan) | Find item: instant |
In One Sentence
Sets store unique items only, making it fast to check membership and find what's common or different between groups.
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