C# 7 and .NET Core 2.0 High Performance

Dictionaries, hashtables, and hashsets

Dictionary, hashtable, and hashset objects store items in key—value format. However, hashsets and dictionaries are good for scenarios where performance is key. Here are a few circumstances where these types are useful:

• To store an item in key–value format that can be retrieved based on a particular key
• To store unique values

The following table shows the Big O notation value for each operation that can be performed on these objects:

Operations	Big O notation
Access	O(n)
Search for the value if the key is not known	O(n)
Insert item	O(n)
Delete item	O(n)