DFS BinaryTree: Pre-Order, In-Order, Post-Order

09_BinaryTreeDFS.swift

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+class Node {
+    var left: Node?
+    var right: Node?
+    var value: Int
+
+    init(value: Int) {
+        self.value = value
+    }
+}
+
+
+// Preorder → process root first.
+func preOrder(_ node: Node?)  {
+    guard let node = node else {
+        return
+    }
+
+    print(node.value)
+    preOrder(node.left)
+    preOrder(node.right)
+}
+
+// Inorder → process root between left and right.
+func inOrder(_ node: Node?) {
+    guard let node = node else {
+        return
+    }
+
+    inOrder(node.left)
+    print(node.value)
+    inOrder(node.right)
+}
+
+// Postorder → process root last.
+func postOrder(_ node: Node?) {
+    guard let node = node else {
+        return
+    }
+    postOrder(node.left)
+    postOrder(node.right)
+    print(node.value)
+}
+
+
+// MARK: Iterative
+
+func preOrderIterative(_ node: Node?) {
+    guard let tempNode = node else { return }
+    var stack = [Node]()
+    stack.append(tempNode)
+
+    while !stack.isEmpty {
+        let poped = stack.removeLast()
+        print(poped.value)
+
+        if let rightE = poped.right {
+            stack.append(rightE)
+        }
+
+        if let leftE = poped.left {
+            stack.append(leftE)
+        }
+    }
+}
+