LINQ to find the closest number that is greater / less than an input

Question

Suppose I have this number list:

List = new List(){3,5,8,11,12,13,14,21}

Suppose that I want to get the closest number th

Answer 1

You can do this using a binary search. If your searching for 11, well obviously you'll get the index your after. If you search for 10 and use the bitwise complement of the result, you'll get the closest match.

   List list = new List(){3,5,8,11,12,13,14,21};

   list.Sort();

   int index = list.BinarySearch(10);

   int found =  (~index)-1;

   Console.WriteLine (list[found]); // Outputs 8

The same goes searching in the other direction

int index = list.BinarySearch(15);

Console.WriteLine("Closest match : " + list[+~index]); // Outputs 21

Binary searches are also extremely fast.