Level order traversal

Trees_LevelOrderTraversal

@@ -0,0 +1,95 @@
+import UIKit
+
+struct Queue<Element> {
+
+    var elements: [Element] = []
+
+    mutating func enqueue(_ value: Element) -> Bool {
+        elements.append(value)
+        return true
+    }
+
+    var isEmpty: Bool {
+        return elements.isEmpty
+    }
+
+    mutating func dequeue() -> Element? {
+        return isEmpty ? nil : elements.removeFirst()
+    }
+}
+
+
+class TreeNode<T> {
+
+    var value: T
+    var children: [TreeNode] = []
+
+    init(_ value: T) {
+        self.value = value
+    }
+
+    func add(_ child: TreeNode) {
+        self.children.append(child)
+    }
+}
+
+extension TreeNode {
+
+    func forEachLevelOrder(_ visit: (TreeNode) -> Void) {
+        visit(self)  //call root node
+
+        var queue = Queue<TreeNode>()
+        children.forEach {
+            queue.enqueue($0)
+        }
+        while let node = queue.dequeue() {
+            visit(node)
+            node.children.forEach {
+                queue.enqueue($0)
+            }
+        }
+    }
+}
+
+/*
+           Beverages
+           /       \
+        Hot         Cold
+       /   \        /   \
+    Tea   Coffee   Soda  Milk
+
+*/
+
+let beverages = TreeNode<String>("Beverages")
+let hot = TreeNode<String>("Hot")
+let cold = TreeNode<String>("Cold")
+beverages.add(hot)
+beverages.add(cold)
+
+let tea = TreeNode<String>("Tea")
+let coffee = TreeNode<String>("Coffee")
+hot.add(tea)
+hot.add(coffee)
+
+let soda = TreeNode<String>("Soda")
+let milk = TreeNode<String>("Milk")
+cold.add(soda)
+cold.add(milk)
+
+
+beverages.forEachLevelOrder {
+    print($0.value)     // level order traversal
+}
+
+
+/* 
+
+Output printed:
+    Beverages
+    Hot
+    Cold
+    Tea
+    Coffee
+    Soda
+    Milk
+*/