CSharp-Coder

C# collections performance compared: List vs Dictionary vs HashSet vs Queue with Big O tables, benchmarks, and code. Learn which collection to use now. Choosing the right C# collections is one of the highest-impact performance decisions you can make in .NET — and one of the most common interview questions for C# developers. Should you use a List<T> , a Dictionary<TKey, TValue> , a HashSet<T> , or a Queue<T> ? Pick wrong, and a lookup that should take nanoseconds turns into a linear scan that melts your CPU at scale. In this C# collections performance guide, we compare all four with Big O complexity tables, runnable code examples, and real-world guidance on when to use each — so you never have to guess again. Why C# Collections Performance Matters Every collection in .NET is a trade-off between memory layout, lookup speed, insertion cost, and ordering guarantees. The difference between List<T>.Contains() and HashSet<T>.Contains() isn't a...