How to save CPU cycles when searching for a value in a sorted list?

Question

In CodinGame learning platform, one of the questions used as an example in a C# tutorial is this one:

The aim of this exercise is to check the presence of

Answer 1

Yes, I think that binary search O(log(N)) complexity v. O(N) complexity is the solution:

   public static bool Exists(int[] ints, int k) {
     return Array.BinarySearch(ints, k) >= 0;
   }

since Array.BinarySearch return non-negative value if the item (k) has been found:

https://msdn.microsoft.com/en-us/library/2cy9f6wb(v=vs.110).aspx

Return Value Type: System.Int32 The index of the specified value in the specified array, if value is found; otherwise, a negative number.