F# and C# addings (#189)

* F# - Binary Search

* C# - Double selection sort

* quick sort - f#

01_introduction_to_algorithms/f#/Program.fs

@@ -0,0 +1,26 @@
+// Learn more about F# at http://fsharp.org
+
+open System
+
+[<EntryPoint>]
+let main argv =
+    let numbers = [|1; 2; 3; 4; 5; 6; 7; 8; 9; 10|]
+
+    let rec binarySearch(arr: int[], number: int, startIndex: int, endIndex: int) : int
+        = 
+            let averageIndex = (startIndex + endIndex) / 2
+            let middleElement = arr.[averageIndex]
+
+            if (middleElement > number)
+                then binarySearch(arr, number, startIndex, averageIndex)
+            else if (middleElement < number)
+                then binarySearch(arr, number, averageIndex, endIndex)
+            else
+                averageIndex
+
+    let binarySearch(arr: int[], number: int)
+        = binarySearch(arr, number, 0, arr.Length)
+
+    let index = binarySearch(numbers, 7)
+    Console.WriteLine(index);
+    0