diff --git a/README.md b/README.md
index 0753db13..ea8c166c 100644
--- a/README.md
+++ b/README.md
@@ -708,6 +708,7 @@ Profile on LeetCode: [fartem](https://leetcode.com/fartem/).
 | 1609. Even Odd Tree                                                                 | [Link](https://leetcode.com/problems/even-odd-tree/)                                                                 | [Link](./lib/medium/1609_even_odd_tree.rb)                                                                 | [Link](./test/medium/test_1609_even_odd_tree.rb)                                                                 |
 | 1630. Arithmetic Subarrays                                                          | [Link](https://leetcode.com/problems/arithmetic-subarrays/)                                                          | [Link](./lib/medium/1630_arithmetic_subarrays.rb)                                                          | [Link](./test/medium/test_1630_arithmetic_subarrays.rb)                                                          |
 | 1641. Count Sorted Vowel Strings                                                    | [Link](https://leetcode.com/problems/count-sorted-vowel-strings/)                                                    | [Link](./lib/medium/1641_count_sorted_vowel_strings.rb)                                                    | [Link](./test/medium/test_1641_count_sorted_vowel_strings.rb)                                                    |
+| 1669. Merge In Between Linked Lists                                                 | [Link](https://leetcode.com/problems/merge-in-between-linked-lists/)                                                 | [Link](./lib/medium/1669_merge_in_between_linked_lists.rb)                                                 | [Link](./test/medium/test_1669_merge_in_between_linked_lists.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)                                                   |
 | 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)                                                                  |
diff --git a/leetcode-ruby.gemspec b/leetcode-ruby.gemspec
index dcdaddce..fc342d7f 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 = '8.7.4'
+  s.version = '8.7.5'
   s.license = 'MIT'
   s.files = ::Dir['lib/**/*.rb'] + %w[README.md]
   s.executable = 'leetcode-ruby'
diff --git a/lib/medium/1669_merge_in_between_linked_lists.rb b/lib/medium/1669_merge_in_between_linked_lists.rb
new file mode 100644
index 00000000..ed1b5fd3
--- /dev/null
+++ b/lib/medium/1669_merge_in_between_linked_lists.rb
@@ -0,0 +1,42 @@
+# frozen_string_literal: true
+
+# https://leetcode.com/problems/merge-in-between-linked-lists/
+# @param {ListNode} list1
+# @param {Integer} a
+# @param {Integer} b
+# @param {ListNode} list2
+# @return {ListNode}
+def merge_in_between(list1, a, b, list2)
+  node_a = nil
+  node_b = nil
+  pointer = list1
+  count = 0
+
+  a -= 1
+  b += 1
+
+  while pointer
+    if count == a
+      node_a = pointer
+    elsif count == b
+      node_b = pointer
+    end
+
+    count += 1
+    pointer = pointer.next
+  end
+
+  return list1 unless node_a
+
+  node_a.next = list2
+
+  if node_b
+    pointer = list2
+
+    pointer = pointer.next while pointer.next
+
+    pointer.next = node_b
+  end
+
+  list1
+end
diff --git a/test/medium/test_1669_merge_in_between_linked_lists.rb b/test/medium/test_1669_merge_in_between_linked_lists.rb
new file mode 100644
index 00000000..ffdae424
--- /dev/null
+++ b/test/medium/test_1669_merge_in_between_linked_lists.rb
@@ -0,0 +1,48 @@
+# frozen_string_literal: true
+
+require_relative '../test_helper'
+require_relative '../../lib/common/linked_list'
+require_relative '../../lib/medium/1669_merge_in_between_linked_lists'
+require 'minitest/autorun'
+
+class MergeInBetweenLinkedListTest < ::Minitest::Test
+  def test_default_one
+    assert(
+      ::ListNode.are_equals(
+        ::ListNode.from_array(
+          [10, 1, 13, 1_000_000, 1_000_001, 1_000_002, 5]
+        ),
+        merge_in_between(
+          ::ListNode.from_array(
+            [10, 1, 13, 6, 9, 5]
+          ),
+          3,
+          4,
+          ::ListNode.from_array(
+            [1_000_000, 1_000_001, 1_000_002]
+          )
+        )
+      )
+    )
+  end
+
+  def test_default_two
+    assert(
+      ::ListNode.are_equals(
+        ::ListNode.from_array(
+          [0, 1, 1_000_000, 1_000_001, 1_000_002, 1_000_003, 1_000_004, 6]
+        ),
+        merge_in_between(
+          ::ListNode.from_array(
+            [0, 1, 2, 3, 4, 5, 6]
+          ),
+          2,
+          5,
+          ::ListNode.from_array(
+            [1_000_000, 1_000_001, 1_000_002, 1_000_003, 1_000_004]
+          )
+        )
+      )
+    )
+  end
+end