diff --git a/climbing-stairs/han.exs b/climbing-stairs/han.exs
new file mode 100644
index 000000000..cecad91e7
--- /dev/null
+++ b/climbing-stairs/han.exs
@@ -0,0 +1,12 @@
+defmodule Solution do
+  @spec climb_stairs(n :: integer) :: integer
+  def climb_stairs(n) do
+      do_climb_stairs(n, 1, 0, 1)
+  end
+
+  defp do_climb_stairs(n, n, n_1, n_2), do: n_1 + n_2
+
+  defp do_climb_stairs(n, step, n_1, n_2) do
+    do_climb_stairs(n, step + 1, n_2, n_1 + n_2)
+  end
+end
diff --git a/maximum-depth-of-binary-tree/han.exs b/maximum-depth-of-binary-tree/han.exs
new file mode 100644
index 000000000..42fe334aa
--- /dev/null
+++ b/maximum-depth-of-binary-tree/han.exs
@@ -0,0 +1,19 @@
+# Definition for a binary tree node.
+#
+# defmodule TreeNode do
+#   @type t :: %__MODULE__{
+#           val: integer,
+#           left: TreeNode.t() | nil,
+#           right: TreeNode.t() | nil
+#         }
+#   defstruct val: 0, left: nil, right: nil
+# end
+
+defmodule Solution do
+  @spec max_depth(root :: TreeNode.t | nil) :: integer
+  def max_depth(nil, max_depth), do: max_depth
+
+  def max_depth(%TreeNode{left: left, right: right}, max_depth \\ 0) do
+    Enum.max([max_depth(left, max_depth + 1), max_depth(right, max_depth + 1)])
+  end
+end
diff --git a/same-tree/han.exs b/same-tree/han.exs
new file mode 100644
index 000000000..611d456ce
--- /dev/null
+++ b/same-tree/han.exs
@@ -0,0 +1,29 @@
+# Definition for a binary tree node.
+#
+# defmodule TreeNode do
+#   @type t :: %__MODULE__{
+#           val: integer,
+#           left: TreeNode.t() | nil,
+#           right: TreeNode.t() | nil
+#         }
+#   defstruct val: 0, left: nil, right: nil
+# end
+#
+# Super simple solution
+# defmodule Solution do
+#   @spec is_same_tree(p :: TreeNode.t | nil, q :: TreeNode.t | nil) :: boolean
+#   def is_same_tree(p, q) do
+#     p == q
+#   end
+# end
+
+defmodule Solution do
+  @spec is_same_tree(p :: TreeNode.t | nil, q :: TreeNode.t | nil) :: boolean
+  def is_same_tree(nil, nil), do: true
+  def is_same_tree(_, nil), do: false
+  def is_same_tree(nil, _), do: false
+
+  def is_same_tree(p, q) do
+    p.val == q.val && is_same_tree(p.left, q.left) && is_same_tree(p.right, q.right)
+  end
+end
diff --git a/subtree-of-another-tree/han.exs b/subtree-of-another-tree/han.exs
new file mode 100644
index 000000000..65db44b91
--- /dev/null
+++ b/subtree-of-another-tree/han.exs
@@ -0,0 +1,21 @@
+# Definition for a binary tree node.
+#
+# defmodule TreeNode do
+#   @type t :: %__MODULE__{
+#           val: integer,
+#           left: TreeNode.t() | nil,
+#           right: TreeNode.t() | nil
+#         }
+#   defstruct val: 0, left: nil, right: nil
+# end
+
+defmodule Solution do
+  @spec is_subtree(root :: TreeNode.t | nil, sub_root :: TreeNode.t | nil) :: boolean
+  def is_subtree(root, root), do: true
+
+  def is_subtree(%TreeNode{left: left, right: right}, sub_root) do
+    is_subtree(left, sub_root) || is_subtree(right, sub_root)
+  end
+
+  def is_subtree(_, _), do: false
+end