add another solution of Invert Binary Tree

Author: za-bannai

go/invert_binary_tree.go

@@ -1,9 +1,28 @@
 //lint:file-ignore U1000 Ignore all unused code
 package main
 
-func invertTree(root *TreeNode) *TreeNode {
+func invertTreeRecursive(root *TreeNode) *TreeNode {
 	if root != nil {
-		root.Left, root.Right = invertTree(root.Right), invertTree(root.Left)
+		root.Left, root.Right = invertTreeRecursive(root.Right), invertTreeRecursive(root.Left)
+	}
+	return root
+}
+
+func invertTreeIterative(root *TreeNode) *TreeNode {
+	if root == nil {
+		return nil
+	}
+	stack := []*TreeNode{root}
+	for len(stack) > 0 {
+		node := stack[len(stack)-1]
+		stack = stack[:len(stack)-1]
+		node.Left, node.Right = node.Right, node.Left
+		if node.Left != nil {
+			stack = append(stack, node.Left)
+		}
+		if node.Right != nil {
+			stack = append(stack, node.Right)
+		}
 	}
 	return root
 }