diff --git a/README.md b/README.md
index bc024470..0f073d4d 100644
--- a/README.md
+++ b/README.md
@@ -608,3 +608,4 @@ Profile on LeetCode: [fartem](https://leetcode.com/fartem/).
 | 662. Maximum Width of Binary Tree                               | [Link](https://leetcode.com/problems/maximum-width-of-binary-tree/)                               | [Link](./lib/medium/662_maximum_width_of_binary_tree.rb)                               | [Link](./test/medium/test_662_maximum_width_of_binary_tree.rb)                               |
 | 669. Trim a Binary Search Tree                                  | [Link](https://leetcode.com/problems/trim-a-binary-search-tree/)                                  | [Link](./lib/medium/669_trim_a_binary_search_tree.rb)                                  | [Link](./test/medium/test_669_trim_a_binary_search_tree.rb)                                  |
 | 677. Map Sum Pairs                                              | [Link](https://leetcode.com/problems/map-sum-pairs/)                                              | [Link](./lib/medium/677_map_sum_pairs.rb)                                              | [Link](./test/medium/test_677_map_sum_pairs.rb)                                              |
+| 678. Valid Parenthesis String                                   | [Link](https://leetcode.com/problems/valid-parenthesis-string/)                                   | [Link](./lib/medium/678_valid_parenthesis_string.rb)                                   | [Link](./test/medium/test_678_valid_parenthesis_string.rb)                                   |
diff --git a/leetcode-ruby.gemspec b/leetcode-ruby.gemspec
index 0de0af34..86004f0b 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 = '7.4.3'
+  s.version = '7.4.4'
   s.license = 'MIT'
   s.files = ::Dir['lib/**/*.rb'] + %w[README.md]
   s.executable = 'leetcode-ruby'
diff --git a/lib/medium/678_valid_parenthesis_string.rb b/lib/medium/678_valid_parenthesis_string.rb
new file mode 100644
index 00000000..2f9198a3
--- /dev/null
+++ b/lib/medium/678_valid_parenthesis_string.rb
@@ -0,0 +1,19 @@
+# frozen_string_literal: true
+
+# https://leetcode.com/problems/valid-parenthesis-string/
+# @param {String} s
+# @return {Boolean}
+def check_valid_string(s)
+  l = 0
+  h = 0
+  s.each_char do |c|
+    l += c == '(' ? 1 : -1
+    h += c == ')' ? -1 : 1
+
+    break if h.negative?
+
+    l = [l, 0].max
+  end
+
+  l.zero?
+end
diff --git a/test/medium/test_678_valid_parenthesis_string.rb b/test/medium/test_678_valid_parenthesis_string.rb
new file mode 100644
index 00000000..23462b31
--- /dev/null
+++ b/test/medium/test_678_valid_parenthesis_string.rb
@@ -0,0 +1,13 @@
+# frozen_string_literal: true
+
+require_relative '../test_helper'
+require_relative '../../lib/medium/678_valid_parenthesis_string'
+require 'minitest/autorun'
+
+class ValidParenthesisStringTest < ::Minitest::Test
+  def test_default_one = assert(check_valid_string('()'))
+
+  def test_default_two = assert(check_valid_string('(*)'))
+
+  def test_default_three = assert(check_valid_string('(*))'))
+end