Partial key match in a sorted List<string>

Say I have a sorted list of strings like {"a1", "a2", "b0", "b2", "c1", ...}开发者_如何学C and want to determine an index of the first element starting from "b". What is the fastest way to get it in .NET 4? Memory is not a problem.

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Use this:

var list = new List<string> { "a1", "a2", "b0", "b2", "c1" };
int index = list.FindIndex(x => x.StartsWith("b"));

If your list is huge and performance is an issue, than consider the answer in the possible duplicate as noted by Joel Rondeau in his comment to your question.

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If for "fastest" you mean "easiest to implement" then

Something roughly like this:

static int FirstIndex(this IEnumerable<T> coll, Predicate<T> pred)
{
    var it = coll.GetEnumerator();

    int index = 0;

    while(it.MoveNext())
    {
        if(pred(it.Current))
        {
           return index;
        }
        index++;
    }

     throw new ObjectNotFoundException();
}    

{"a1", "a2", "b0", "b2", "c1"}.FirstIndex(s => s.StartsWith("b"));

Or using the Seq module from F# (caveat, I've never tried using these from C#... this syntax is probably wrong.):

Seq.findIndex(s => s.StartsWith("b"))(strings);