Day 76: Set vs Map – When and Why to Use Each in JavaScript
When solving DSA problems or building real-world apps, choosing between a Set and a Map can feel trivial—but it’s not. 
These two data structures serve different purposes, and knowing when to use which can make your code cleaner and faster.
Map: The Lookup King 
Stores key-value pairs
Keys can be any data type
Keeps insertion order
Access time: O(1)
Use a Map when:
You need to associate values with keys
You need quick lookups based on a key
You want to track counts, indices, or flags
js
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const map = new Map();
map.set(‘apple’, 2);
map.get(‘apple’); // 2
Set: The Uniqueness Guardian 
Stores only values
Each value must be unique
Also keeps insertion order
Access time: O(1)
Use a Set when:
You just need to store unique items
You want to check existence fast
You’re cleaning duplicates or tracking seen elements
js
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const set = new Set([1, 2, 2, 3]);
console.log(set); // Set {1, 2, 3}
Real DSA Examples
Use a Set in Longest Substring Without Repeating Characters
Use a Map in Two Sum, Group Anagrams, Top K Frequent Elements
Quick Summary:
Use Case Set Map
Unique values only 
Yes 
No
Key-value pairs No Yes
Fast lookup Yes Yes
Track frequency/index Yes
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