diff --git a/README.md b/README.md
index f08882c2..ca0654c5 100644
--- a/README.md
+++ b/README.md
@@ -630,6 +630,7 @@ Profile on LeetCode: [fartem](https://leetcode.com/fartem/).
 | 856. Score of Parentheses                                       | [Link](https://leetcode.com/problems/score-of-parentheses/)                                       | [Link](./lib/medium/856_score_of_parentheses.rb)                                       | [Link](./test/medium/test_856_score_of_parentheses.rb)                                       |
 | 858. Mirror Reflection                                          | [Link](https://leetcode.com/problems/mirror-reflection/)                                          | [Link](./lib/medium/858_mirror_reflection.rb)                                          | [Link](./test/medium/test_858_mirror_reflection.rb)                                          |
 | 863. All Nodes Distance K in Binary Tree                        | [Link](https://leetcode.com/problems/all-nodes-distance-k-in-binary-tree/)                        | [Link](./lib/medium/863_all_nodes_distance_k_in_binary_tree.rb)                        | [Link](./test/medium/test_863_all_nodes_distance_k_in_binary_tree.rb)                        |
+| 865. Smallest Subtree with all the Deepest Nodes                | [Link](https://leetcode.com/problems/smallest-subtree-with-all-the-deepest-nodes/)                | [Link](./lib/medium/865_smallest_subtree_with_all_the_deepest_nodes.rb)                | [Link](./test/medium/test_865_smallest_subtree_with_all_the_deepest_nodes.rb)                |
 
 ### Hard
 
diff --git a/leetcode-ruby.gemspec b/leetcode-ruby.gemspec
index caf25728..f8333082 100644
--- a/leetcode-ruby.gemspec
+++ b/leetcode-ruby.gemspec
@@ -5,7 +5,7 @@ require 'English'
 ::Gem::Specification.new do |s|
   s.required_ruby_version = '>= 3.0'
   s.name = 'leetcode-ruby'
-  s.version = '7.7.3.1'
+  s.version = '7.7.4'
   s.license = 'MIT'
   s.files = ::Dir['lib/**/*.rb'] + %w[README.md]
   s.executable = 'leetcode-ruby'
diff --git a/lib/medium/865_smallest_subtree_with_all_the_deepest_nodes.rb b/lib/medium/865_smallest_subtree_with_all_the_deepest_nodes.rb
new file mode 100644
index 00000000..0fb43106
--- /dev/null
+++ b/lib/medium/865_smallest_subtree_with_all_the_deepest_nodes.rb
@@ -0,0 +1,37 @@
+# frozen_string_literal: true
+
+# https://leetcode.com/problems/smallest-subtree-with-all-the-deepest-nodes/
+# @param {TreeNode} root
+# @return {TreeNode}
+def subtree_with_all_deepest(root)
+  dfs_for_smallest_subtree(root, depth_for_smallest_subtree(root))
+end
+
+private
+
+# @param {TreeNode} node
+# @return {Integer}
+def depth_for_smallest_subtree(node)
+  return 0 unless node
+
+  left = depth_for_smallest_subtree(node.left)
+  right = depth_for_smallest_subtree(node.right)
+
+  1 + [left, right].max
+end
+
+# @param {TreeNode} node
+# @param {Integer} depth
+# @return {TreeNode}
+def dfs_for_smallest_subtree(node, depth)
+  return unless node
+
+  return node if depth == 1
+
+  left = dfs_for_smallest_subtree(node.left, depth - 1)
+  right = dfs_for_smallest_subtree(node.right, depth - 1)
+
+  return node if left && right
+
+  left.nil? ? right : left
+end
diff --git a/test/medium/test_865_smallest_subtree_with_all_the_deepest_nodes.rb b/test/medium/test_865_smallest_subtree_with_all_the_deepest_nodes.rb
new file mode 100644
index 00000000..b7ad47f4
--- /dev/null
+++ b/test/medium/test_865_smallest_subtree_with_all_the_deepest_nodes.rb
@@ -0,0 +1,65 @@
+# frozen_string_literal: true
+
+require_relative '../test_helper'
+require_relative '../../lib/common/binary_tree'
+require_relative '../../lib/medium/865_smallest_subtree_with_all_the_deepest_nodes'
+require 'minitest/autorun'
+
+class SmallestSubtreeWithAllTheDeepestNodesTest < ::Minitest::Test
+  def test_default_one
+    target = ::TreeNode.new(
+      2,
+      ::TreeNode.new(7),
+      ::TreeNode.new(4)
+    )
+
+    assert_equal(
+      target,
+      subtree_with_all_deepest(
+        ::TreeNode.new(
+          3,
+          ::TreeNode.new(
+            5,
+            ::TreeNode.new(6),
+            target
+          ),
+          ::TreeNode.new(
+            1,
+            ::TreeNode.new(0),
+            ::TreeNode.new(8)
+          )
+        )
+      )
+    )
+  end
+
+  def test_default_two
+    target = ::TreeNode.new(1)
+
+    assert_equal(
+      target,
+      subtree_with_all_deepest(
+        target
+      )
+    )
+  end
+
+  def test_default_three
+    target = ::TreeNode.new(2)
+
+    assert_equal(
+      target,
+      subtree_with_all_deepest(
+        ::TreeNode.new(
+          0,
+          ::TreeNode.new(
+            1,
+            nil,
+            target
+          ),
+          ::TreeNode.new(3)
+        )
+      )
+    )
+  end
+end