Added public init and array init

I added a public init so this can be used in a Playground. I also added
an extension to create a linked list from an array of values.

Author: RedQueenCoder

Linked List/LinkedList.playground/Contents.swift

@@ -187,6 +187,16 @@ extension LinkedList {
   }
 }
 
+extension LinkedList {
+  convenience init(array: Array<T>) {
+    self.init()
+        
+    for element in array {
+      self.append(element)
+    }
+  }
+}
+
 let list = LinkedList<String>()
 list.isEmpty                  // true
 list.first                    // nil

Linked List/LinkedList.swift

@@ -12,7 +12,9 @@ public class LinkedList<T> {
   public typealias Node = LinkedListNode<T>
 
   fileprivate var head: Node?
-  
+    
+  public init() {}
+    
   public var isEmpty: Bool {
     return head == nil
   }
@@ -184,3 +186,13 @@ extension LinkedList {
     return result
   }
 }
+
+extension LinkedList {
+  convenience init(array: Array<T>) {
+    self.init()
+        
+    for element in array {
+      self.append(element)
+    }
+  }
+}