Merge branch 'master' into HashSet-Swift4

Author: vincentngo

.travis.yml

@@ -1,5 +1,5 @@
 language: objective-c
-osx_image: xcode8.3
+osx_image: xcode9
 # sudo: false
 
 install:

Array2D/Array2D.playground/Contents.swift

@@ -1,3 +1,8 @@
+// last checked with Xcode 9.0b4
+#if swift(>=4.0)
+print("Hello, Swift 4!")
+#endif
+
 /*
  Two-dimensional array with a fixed number of rows and columns.
  This is mostly handy for games that are played on a grid, such as chess.

Binary Search Tree/Solution 1/BinarySearchTree.playground/Contents.swift

@@ -1,5 +1,10 @@
 //: Playground - noun: a place where people can play
 
+// last checked with Xcode 9.0b4
+#if swift(>=4.0)
+print("Hello, Swift 4!")
+#endif
+
 let tree = BinarySearchTree<Int>(value: 7)
 tree.insert(value: 2)
 tree.insert(value: 5)

Binary Search Tree/Solution 1/BinarySearchTree.playground/timeline.xctimeline

@@ -1,5 +1,10 @@
 //: Playground - noun: a place where people can play
 
+// last checked with Xcode 9.0b4
+#if swift(>=4.0)
+print("Hello, Swift 4!")
+#endif
+
 // Each time you insert something, you get back a completely new tree.
 var tree = BinarySearchTree.leaf(7)
 tree = tree.insert(newValue: 2)

Binary Search Tree/Solution 2/BinarySearchTree.playground/Contents.swift

@@ -1,5 +1,10 @@
 //: Playground - noun: a place where people can play
 
+// last checked with Xcode 9.0b4
+#if swift(>=4.0)
+print("Hello, Swift 4!")
+#endif
+
 // An unsorted array of numbers
 let numbers = [11, 59, 3, 2, 53, 17, 31, 7, 19, 67, 47, 13, 37, 61, 29, 43, 5, 41, 23]
 

Binary Search Tree/Solution 2/BinarySearchTree.playground/timeline.xctimeline

@@ -1,5 +1,10 @@
 //: Playground - noun: a place where people can play
 
+// last checked with Xcode 9.0b4
+#if swift(>=4.0)
+print("Hello, Swift 4!")
+#endif
+
 public indirect enum BinaryTree<T> {
   case node(BinaryTree<T>, T, BinaryTree<T>)
   case empty

Binary Search/BinarySearch.playground/Contents.swift

@@ -1,3 +1,8 @@
+// last checked with Xcode 9.0b4
+#if swift(>=4.0)
+print("Hello, Swift 4!")
+#endif
+
 func breadthFirstSearch(_ graph: Graph, source: Node) -> [String] {
   var queue = Queue<Node>()
   queue.enqueue(source)