Best Collection for Fast String Lookup

Question

I need a list of strings and a way to quickly determine if a string is contained within that list.

To enhance lookup speed, I considered SortedList and

Answer 1

If you're on .NET 3.5 or higher, use HashSet<String>.

Failing that, a Dictionary<string, byte> (or whatever type you want for the TValue type parameter) would be faster than a SortedList if you have a lot of entries - the latter will use a binary search, so it'll be O(log n) lookup, instead of O(1).

Answer 2

If you feel like rolling your own data structure, use a Trie. http://en.wikipedia.org/wiki/Trie

worst-case is if the string is present: O(length of string)

Answer 3

HashSet<string> is like a Dictionary, but with only keys.

Answer 4

I know the question is old as hell, but I just had to solve the same problem, only for a very small set of strings(between 2 and 4).

In my case, I actually used manual lookup over an array of strings which turned up to be much faster than HashSet<string>(I benchmarked it).

for (int i = 0; i < this.propertiesToIgnore.Length; i++)
{
    if (this.propertiesToIgnore[i].Equals(propertyName))
    {
        return true;
    }
}

Note, that it is better than hash set for only for tiny arrays!

EDIT: works only with a manual for loop, do not use LINQ, details in comments

Answer 5

This sounds like a job for

 var keys = new HashSet<string>();

Per MSDN: The Contains function has O(1) complexity.

But you should be aware that it does not give an error for duplicates when adding.

Answer 6

If you just want to know if a string is in the set use HashSet<string>