Can LINQ be used to find gaps in a sorted list?

Question

Is it possible for me to use LINQ in a way that allows me to determine that \"9\" is the first missing value in the sorted list without using a for-loop and comparing each

Answer 1

(abatishchev beat me to the punch, but his answer is better anyway. However, since alternate solutions to the same problem can be fun, I am still posting this.)

Hackity hack hack. But working, if you really want to do this. Performance will be awful, because this technique will not stop when it finds the answer -- it will always loop over every number! But it will work:

public static int FindFirstMissing(IEnumerable sequence)
{
    bool found = false;

    int agg = sequence.Aggregate((aggregate, next) => {
        if (found)
            return aggregate;

        if (next - aggregate != 1) {
            found = true;
            return aggregate + 1;
        }

        return next;
    });

    if (!found)
        throw new ArgumentException("sequence", "Contains no missing numbers.");

    return agg;
}