What are the common C# collections?

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**Collections** — data structures for storing and managing data. **List:** ```csharp var list = new List { 1, 2, 3 }; list.Add(4); // O(1) amortized list.Remove(1); // O(n) list.Contains(2); // O(n) ``` **Dictionary:** ```csharp var dict = new Dictionary(); dict["one"] = 1; // O(1) dict.TryGetValue("one", out var val); // O(1) dict.Remove("one"); // O(1) ``` **HashSet:** ```csharp var set = new HashSet { 1, 2, 3 }; set.Add(1); // false (already exists) set.Contains(1); // O(1) ``` **Queue:** ```csharp var queue = new Queue(); queue.Enqueue("first"); // O(1) queue.Dequeue(); // O(1) queue.Peek(); // O(1) ``` **Stack:** ```csharp var stack = new Stack(); stack.Push("first"); // O(1) stack.Pop(); // O(1) stack.Peek(); // O(1) ```

C#: What are the common C# collections?