DSA in DartBeginner10 XP3 min read
What are the main collection types in Dart and when do you use each?
TL;DR: List: ordered, indexed, allows duplicates (O(1) access by index). Set: unordered, unique elements (O(1) lookup). Map: key-value pairs (O(1) lookup by key). Queue: efficient add/remove from both ends.
Full Answer
| Aspect | Collection | Characteristics |
|---|---|---|
| List<T> | Ordered, duplicates, index access | O(1) get, O(n) search, O(1) add to end |
| Set<T> | Unordered, unique elements (HashSet) | O(1) contains, add, remove |
| Map<K,V> | Key-value pairs, unique keys (HashMap) | O(1) lookup, add, remove by key |
| Queue<T> | Ordered, efficient both-end ops | O(1) addFirst, addLast, removeFirst |
🎯
Use Set for checking membership (contains) — it's O(1) vs List's O(n). If you check 'is this ID in the list' frequently, convert to a Set.
Code Examples
dartChoosing the right collection
Output
// Set.contains: O(1) vs List.contains: O(n) // Map lookup: O(1) vs searching List of objects: O(n)
Common Mistakes
- ✗Using List.contains() in a hot path when Set.contains() is O(1)
- ✗Using Map.values.toList() when you just need to iterate — .values already is iterable
Interview Tip
💡
Show you know the time complexities. The most impactful optimization is often replacing a List.contains() in a loop (O(n²)) with a Set.contains() (O(n)).
#list#set#map#queue#collections