What's the most efficient way to get a first free spot from sorted query returning int collection ?
eg.: {1,2,3,4,6} | result.: 5
At the moment I am using foreach and counter that compares current value from sorted quety.ToList() which takes about 600ms on 100 000 records.
Unless you multithread it, reading one at a time is your fastest solution since this is an O(n) problem.
I am not sure how you would write it in LINQ, but I suppose a binary search could be faster in this way - starting from the middle, comparing the index with value - if they are equal, continue in the right half, otherwise in the left half etc.
Even if you're starting from an index start_index which is not 1, you can simply compare the value with index increased by start_index.
Why do you use ToList()? Turning it to a list renders the whole IEnumerable idea absolute and you might lose some performance there. Why not iterate with foreach over the IQueryable and find the first missing memeber?