add new solutions

solutions/2/q226/solution.go

@@ -0,0 +1,17 @@
+package q226
+
+type TreeNode struct {
+	Val   int
+	Left  *TreeNode
+	Right *TreeNode
+}
+
+func invertTree(root *TreeNode) *TreeNode {
+	if root == nil {
+		return nil
+	}
+	root.Left, root.Right = root.Right, root.Left
+	invertTree(root.Left)
+	invertTree(root.Right)
+	return root
+}