diff --git a/README.md b/README.md
index 45840549..aa4d2c2c 100644
--- a/README.md
+++ b/README.md
@@ -746,6 +746,7 @@ Profile on LeetCode: [fartem](https://leetcode.com/fartem/).
 | 2177. Find Three Consecutive Integers That Sum to a Given Number                    | [Link](https://leetcode.com/problems/find-three-consecutive-integers-that-sum-to-a-given-number/)                    | [Link](./lib/medium/2177_find_three_consecutive_integers_that_sum_to_a_given_number.rb)                    | [Link](./test/medium/test_2177_find_three_consecutive_integers_that_sum_to_a_given_number.rb)                    |
 | 2181. Merge Nodes in Between Zeros                                                  | [Link](https://leetcode.com/problems/merge-nodes-in-between-zeros/)                                                  | [Link](./lib/medium/2181_merge_nodes_in_between_zeros.rb)                                                  | [Link](./test/medium/test_2181_merge_nodes_in_between_zeros.rb)                                                  |
 | 2196. Create Binary Tree From Descriptions                                          | [Link](https://leetcode.com/problems/create-binary-tree-from-descriptions/)                                          | [Link](./lib/medium/2196_create_binary_tree_from_descriptions.rb)                                          | [Link](./test/medium/test_2196_create_binary_tree_from_descriptions.rb)                                          |
+| 2221. Find Triangular Sum of an Array                                               | [Link](https://leetcode.com/problems/find-triangular-sum-of-an-array/)                                               | [Link](./lib/medium/2221_find_triangular_sum_of_an_array.rb)                                               | [Link](./test/medium/test_2221_find_triangular_sum_of_an_array.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)                                                   |
 | 2429. Minimize XOR                                                                  | [Link](https://leetcode.com/problems/minimize-xor/)                                                                  | [Link](./lib/medium/2429_minimize_xor.rb)                                                                  | [Link](./test/medium/test_2429_minimize_xor.rb)                                                                  |
 | 2657. Find the Prefix Common Array of Two Arrays                                    | [Link](https://leetcode.com/problems/find-the-prefix-common-array-of-two-arrays/)                                    | [Link](./lib/medium/2657_find_the_prefix_common_array_of_two_arrays.rb)                                    | [Link](./test/medium/test_2657_find_the_prefix_common_array_of_two_arrays.rb)                                    |
diff --git a/leetcode-ruby.gemspec b/leetcode-ruby.gemspec
index b0232189..4d0695b6 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 = '9.1.1'
+  s.version = '9.1.2'
   s.license = 'MIT'
   s.files = ::Dir['lib/**/*.rb'] + %w[README.md]
   s.executable = 'leetcode-ruby'
diff --git a/lib/medium/2221_find_triangular_sum_of_an_array.rb b/lib/medium/2221_find_triangular_sum_of_an_array.rb
new file mode 100644
index 00000000..9574295b
--- /dev/null
+++ b/lib/medium/2221_find_triangular_sum_of_an_array.rb
@@ -0,0 +1,18 @@
+# frozen_string_literal: true
+
+# https://leetcode.com/problems/find-triangular-sum-of-an-array/
+# @param {Integer[]} nums
+# @return {Integer}
+def triangular_sum(nums)
+  count = nums.size
+
+  until count == 1
+    (0...(count - 1)).each do |i|
+      nums[i] = (nums[i] + nums[i + 1]) % 10
+    end
+
+    count -= 1
+  end
+
+  nums.first
+end
diff --git a/test/medium/test_2221_find_triangular_sum_of_an_array.rb b/test/medium/test_2221_find_triangular_sum_of_an_array.rb
new file mode 100644
index 00000000..f049dbc4
--- /dev/null
+++ b/test/medium/test_2221_find_triangular_sum_of_an_array.rb
@@ -0,0 +1,25 @@
+# frozen_string_literal: true
+
+require_relative '../test_helper'
+require_relative '../../lib/medium/2221_find_triangular_sum_of_an_array'
+require 'minitest/autorun'
+
+class FindTriangularSumOfAnArrayTest < ::Minitest::Test
+  def test_default_one
+    assert_equal(
+      8,
+      triangular_sum(
+        [1, 2, 3, 4, 5]
+      )
+    )
+  end
+
+  def test_default_two
+    assert_equal(
+      5,
+      triangular_sum(
+        [5]
+      )
+    )
+  end
+end