Count Occurrences to Swift 4

Tested Count Occurrences with Swift 4 and Xcode 9.0b4

Author: bobdel

Count Occurrences/CountOccurrences.playground/Contents.swift

@@ -1,4 +1,7 @@
-//: Playground - noun: a place where people can play
+// last checked with Xcode 9.0b4
+#if swift(>=4.0)
+  print("Hello, Swift 4!")
+#endif
 
 func countOccurrencesOfKey(_ key: Int, inArray a: [Int]) -> Int {
   func leftBoundary() -> Int {