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System.Collections.Generic

Core Generic Collections

List<T>​

Resizable dynamic array.
Fast random access (O(1)), append is amortized O(1).

Dictionary<TKey, TValue>​

Hash map (hash table).
Fast lookup/insert/delete average O(1).

HashSet<T>​

Unique-value collection (mathematical set).
Insert & lookup average O(1).

Queue<T>​

FIFO (First-In-First-Out) collection.

Stack<T>​

LIFO (Last-In-First-Out) collection.

LinkedList<T>​

Doubly linked list.
Efficient insertion/removal in the middle of the list.

SortedList<TKey, TValue>​

Sorted Key–Value pairs backed by array.
Good for smaller datasets.

SortedDictionary<TKey, TValue>​

Sorted Key–Value pairs backed by red-black tree.
Good for larger datasets.

SortedSet<T>​

Sorted unique elements.
Uses balanced tree (RB-tree).

KeyValuePair<TKey, TValue>​

Struct used when iterating Dictionary<K, V>.