diff --git a/README.md b/README.md
index a31af4e2..b277a9d6 100644
--- a/README.md
+++ b/README.md
@@ -646,6 +646,7 @@ Profile on LeetCode: [fartem](https://leetcode.com/fartem/).
 | 946. Validate Stack Sequences                                    | [Link](https://leetcode.com/problems/validate-stack-sequences/)                                    | [Link](./lib/medium/946_validate_stack_sequences.rb)                                    | [Link](./test/medium/test_946_validate_stack_sequences.rb)                                    |
 | 950. Reveal Cards In Increasing Order                            | [Link](https://leetcode.com/problems/reveal-cards-in-increasing-order/)                            | [Link](./lib/medium/950_reveal_cards_in_increasing_order.rb)                            | [Link](./test/medium/test_950_reveal_cards_in_increasing_order.rb)                            |
 | 951. Flip Equivalent Binary Trees                                | [Link](https://leetcode.com/problems/flip-equivalent-binary-trees/)                                | [Link](./lib/medium/951_flip_equivalent_binary_trees.rb)                                | [Link](./test/medium/test_951_flip_equivalent_binary_trees.rb)                                |
+| 958. Check Completeness of a Binary Tree                         | [Link](https://leetcode.com/problems/check-completeness-of-a-binary-tree/)                         | [Link](./lib/medium/958_check_completeness_of_a_binary_tree.rb)                         | [Link](./test/medium/test_958_check_completeness_of_a_binary_tree.rb)                         |
 | 1400. Construct K Palindrome Strings                             | [Link](https://leetcode.com/problems/construct-k-palindrome-strings/)                              | [Link](./lib/medium/1400_construct_k_palindrome_strings.rb)                             | [Link](./test/medium/test_1400_construct_k_palindrome_strings.rb)                             |
 | 2116. Check if a Parentheses String Can Be Valid                 | [Link](https://leetcode.com/problems/check-if-a-parentheses-string-can-be-valid/)                  | [Link](./lib/medium/2116_check_if_a_parentheses_string_can_be_valid.rb)                 | [Link](./test/medium/test_2116_check_if_a_parentheses_string_can_be_valid.rb)                 |
 | 2425. Bitwise XOR of All Pairings                                | [Link](https://leetcode.com/problems/bitwise-xor-of-all-pairings/)                                 | [Link](./lib/medium/2425_bitwise_xor_of_all_pairings.rb)                                | [Link](./test/medium/test_2425_bitwise_xor_of_all_pairings.rb)                                |
diff --git a/leetcode-ruby.gemspec b/leetcode-ruby.gemspec
index a1e50d03..e6372e99 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 = '8.1.0'
+  s.version = '8.1.1'
   s.license = 'MIT'
   s.files = ::Dir['lib/**/*.rb'] + %w[README.md]
   s.executable = 'leetcode-ruby'
diff --git a/lib/medium/958_check_completeness_of_a_binary_tree.rb b/lib/medium/958_check_completeness_of_a_binary_tree.rb
new file mode 100644
index 00000000..578effd6
--- /dev/null
+++ b/lib/medium/958_check_completeness_of_a_binary_tree.rb
@@ -0,0 +1,24 @@
+# frozen_string_literal: true
+
+# https://leetcode.com/problems/check-completeness-of-a-binary-tree/
+# @param {TreeNode} root
+# @return {Boolean}
+def is_complete_tree(root)
+  is_end = false
+  queue = [root]
+
+  until queue.empty?
+    curr = queue.shift
+
+    if curr
+      return false if is_end
+
+      queue << curr.left
+      queue << curr.right
+    else
+      is_end = true
+    end
+  end
+
+  true
+end
diff --git a/test/medium/test_958_check_completeness_of_a_binary_tree.rb b/test/medium/test_958_check_completeness_of_a_binary_tree.rb
new file mode 100644
index 00000000..7b29bc70
--- /dev/null
+++ b/test/medium/test_958_check_completeness_of_a_binary_tree.rb
@@ -0,0 +1,48 @@
+# frozen_string_literal: true
+
+require_relative '../test_helper'
+require_relative '../../lib/common/binary_tree'
+require_relative '../../lib/medium/958_check_completeness_of_a_binary_tree'
+require 'minitest/autorun'
+
+class CheckCompletenessOfABinaryTreeTest < ::Minitest::Test
+  def test_default_one
+    assert(
+      is_complete_tree(
+        ::TreeNode.new(
+          1,
+          ::TreeNode.new(
+            2,
+            ::TreeNode.new(4),
+            ::TreeNode.new(5)
+          ),
+          ::TreeNode.new(
+            3,
+            ::TreeNode.new(6),
+            nil
+          )
+        )
+      )
+    )
+  end
+
+  def test_default_two
+    assert(
+      !is_complete_tree(
+        ::TreeNode.new(
+          1,
+          ::TreeNode.new(
+            2,
+            ::TreeNode.new(4),
+            ::TreeNode.new(5)
+          ),
+          ::TreeNode.new(
+            3,
+            nil,
+            ::TreeNode.new(7)
+          )
+        )
+      )
+    )
+  end
+end