diff --git a/README.md b/README.md
index 459145ff..7a1114da 100644
--- a/README.md
+++ b/README.md
@@ -666,6 +666,7 @@ Profile on LeetCode: [fartem](https://leetcode.com/fartem/).
 | 1111. Maximum Nesting Depth of Two Valid Parentheses Strings     | [Link](https://leetcode.com/problems/maximum-nesting-depth-of-two-valid-parentheses-strings/)      | [Link](./lib/medium/1111_maximum_nesting_depth_of_two_valid_parentheses_strings.rb)     | [Link](./test/medium/test_1111_maximum_nesting_depth_of_two_valid_parentheses_strings.rb)     |
 | 1123. Lowest Common Ancestor of Deepest Leaves                   | [Link](https://leetcode.com/problems/lowest-common-ancestor-of-deepest-leaves/)                    | [Link](./lib/medium/1123_lowest_common_ancestor_of_deepest_leaves.rb)                   | [Link](./test/medium/test_1123_lowest_common_ancestor_of_deepest_leaves.rb)                   |
 | 1161. Maximum Level Sum of a Binary Tree                         | [Link](https://leetcode.com/problems/maximum-level-sum-of-a-binary-tree/)                          | [Link](./lib/medium/1161_maximum_level_sum_of_a_binary_tree.rb)                         | [Link](./test/medium/test_1161_maximum_level_sum_of_a_binary_tree.rb)                         |
+| 1209. Remove All Adjacent Duplicates in String II                | [Link](https://leetcode.com/problems/remove-all-adjacent-duplicates-in-string-ii/)                 | [Link](./lib/medium/1209_remove_all_adjacent_duplicates_in_string_ii.rb)                | [Link](./test/medium/test_1209_remove_all_adjacent_duplicates_in_string_ii.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 a561b987..5f87c9d9 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 = '8.3.3'
+  s.version = '8.3.4'
   s.license = 'MIT'
   s.files = ::Dir['lib/**/*.rb'] + %w[README.md]
   s.executable = 'leetcode-ruby'
diff --git a/lib/medium/1209_remove_all_adjacent_duplicates_in_string_ii.rb b/lib/medium/1209_remove_all_adjacent_duplicates_in_string_ii.rb
new file mode 100644
index 00000000..167ed3b0
--- /dev/null
+++ b/lib/medium/1209_remove_all_adjacent_duplicates_in_string_ii.rb
@@ -0,0 +1,23 @@
+# frozen_string_literal: true
+
+# https://leetcode.com/problems/remove-all-adjacent-duplicates-in-string-ii/
+# @param {String} s
+# @param {Integer} k
+# @return {String}
+def remove_duplicates_adjacent(s, k)
+  stack = []
+
+  s.each_char do |c|
+    if !stack.empty? && c == stack.last[0]
+      if stack.last[1] == k - 1
+        stack.pop
+      else
+        stack.last[1] += 1
+      end
+    else
+      stack << [c, 1]
+    end
+  end
+
+  stack.map { |char, count| char * count }.join
+end
diff --git a/test/medium/test_1209_remove_all_adjacent_duplicates_in_string_ii.rb b/test/medium/test_1209_remove_all_adjacent_duplicates_in_string_ii.rb
new file mode 100644
index 00000000..6ec5cc6e
--- /dev/null
+++ b/test/medium/test_1209_remove_all_adjacent_duplicates_in_string_ii.rb
@@ -0,0 +1,37 @@
+# frozen_string_literal: true
+
+require_relative '../test_helper'
+require_relative '../../lib/medium/1209_remove_all_adjacent_duplicates_in_string_ii'
+require 'minitest/autorun'
+
+class RemoveAllAdjacentDuplicatesInStringIITest < ::Minitest::Test
+  def test_default_one
+    assert_equal(
+      'abcd',
+      remove_duplicates_adjacent(
+        'abcd',
+        2
+      )
+    )
+  end
+
+  def test_default_two
+    assert_equal(
+      'aa',
+      remove_duplicates_adjacent(
+        'deeedbbcccbdaa',
+        3
+      )
+    )
+  end
+
+  def test_default_three
+    assert_equal(
+      'ps',
+      remove_duplicates_adjacent(
+        'pbbcggttciiippooaais',
+        2
+      )
+    )
+  end
+end