search List for string .StartsWith()

Question

I have a

List

with 1500 strings. I am now using the following code to pull out only string that start with the string prefix

Answer 1

I assume that the really fastest way would be to generate a dictionary with all possible prefixes from your 1500 strings, effectively precomputing the results for all possible searches that will return non-empty. Your search would then be simply a dictionary lookup completing in O(1) time. This is a case of trading memory (and initialization time) for speed.

private IDictionary prefixedStrings;

public void Construct(IEnumerable strings)
{
    this.prefixedStrings =
        (
            from s in strings
            from i in Enumerable.Range(1, s.Length)
            let p = s.Substring(0, i)
            group s by p
        ).ToDictionary(
            g => g.Key,
            g => g.ToArray());
}

public string[] Search(string prefix)
{
    string[] result;
    if (this.prefixedStrings.TryGetValue(prefix, out result))
        return result;

    return new string[0];
}