Best lookup data structure to store only the keys (Dictionary without value)
c#, collections, data-structures, dictionary
Solution
A `HashSet` (in `System.Collections.Generic`):
HashSet is an unordered collection containing unique elements. It has the standard collection operations Add, Remove, Contains, but since it uses a hash-based implementation, these operation are O(1).
e.g.
HashSet<int> evenNumbers = new HashSet<int>();
HashSet<int> oddNumbers = new HashSet<int>();
for (int i = 0; i < 5; i++)
{
// Populate numbers with just even numbers.
evenNumbers.Add(i * 2);
// Populate oddNumbers with just odd numbers.
oddNumbers.Add((i * 2) + 1);
}
if (evenNumbers.Contains(2))
{
Console.WriteLine("2 is even.");
}
- Introducing HashSet
- HashSet vs. List performance
Problem
What is the best data structure in .Net with high performance lookup, like a binary tree implementation, but to store only the keys (string keys) ? We need only to check if a certain key is present in the collection. Like: ``` Dictonary<string, object> myKeys; myKeys.Add("key1", null); myKeys.Add("key2", null); // Dozens or hundreds keys Assert.IsTrue(myKeys.Contains("key1")); ```