diff --git a/.github/workflows/checks.yml b/.github/workflows/checks.yml
index 3f2f95ac..b914c56f 100644
--- a/.github/workflows/checks.yml
+++ b/.github/workflows/checks.yml
@@ -7,7 +7,7 @@ on:
     branches: [ master ]
 
 env:
-  RUBY_VERSION: 3.0
+  RUBY_VERSION: 3.3.6
   SIMPLECOV_THRESHOLD: 100
 
 jobs:
diff --git a/leetcode-ruby.gemspec b/leetcode-ruby.gemspec
index ad8f5d6a..882b5463 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 = '7.5.1'
+  s.version = '7.5.1.1'
   s.license = 'MIT'
   s.files = ::Dir['lib/**/*.rb'] + %w[README.md]
   s.executable = 'leetcode-ruby'
diff --git a/lib/common/linked_list.rb b/lib/common/linked_list.rb
index c94fdb82..333f1ced 100644
--- a/lib/common/linked_list.rb
+++ b/lib/common/linked_list.rb
@@ -29,9 +29,9 @@ def self.from_array(values)
   # @param {ListNode} second
   # @return {Boolean}
   def self.are_equals(first, second)
-    return true if first.nil? && second.nil?
+    return true if !first && !second
 
-    return false if first.nil? || second.nil?
+    return false if !first || !second
 
     first.val == second.val && are_equals(first.next, second.next)
   end
diff --git a/lib/common/list_node_with_random.rb b/lib/common/list_node_with_random.rb
index 07da5ae7..dbd73a40 100644
--- a/lib/common/list_node_with_random.rb
+++ b/lib/common/list_node_with_random.rb
@@ -26,6 +26,6 @@ def self.are_equal(l1, l2)
       l2 = l2.next
     end
 
-    l1.nil? && l2.nil?
+    !l1 && !l2
   end
 end
diff --git a/lib/common/next_tree_node.rb b/lib/common/next_tree_node.rb
index 1475c19d..4611972a 100644
--- a/lib/common/next_tree_node.rb
+++ b/lib/common/next_tree_node.rb
@@ -25,7 +25,7 @@ def self.are_equals(n1, n2)
       return are_equals(n1.left, n2.left) && are_equals(n1.right, n2.right)
     end
 
-    n1.nil? && n2.nil?
+    !n1 && !n2
   end
 
   # @param {NextTreeNode} other
@@ -40,7 +40,5 @@ def ==(other)
   end
 
   # @return {Integer}
-  def hash
-    [val, left, right, nxt].hash
-  end
+  def hash = [val, left, right, nxt].hash
 end
diff --git a/lib/common/node_with_neighbors.rb b/lib/common/node_with_neighbors.rb
index e47bb667..086e4603 100644
--- a/lib/common/node_with_neighbors.rb
+++ b/lib/common/node_with_neighbors.rb
@@ -15,7 +15,7 @@ def initialize(val, neighbors = nil)
   # @param {NodeWithNeighbors} n2
   # @return {Boolean}
   def self.are_equals(n1, n2)
-    if !n1.nil? && !n2.nil?
+    if n1 && n2
       return false unless n1.val == n2.val
 
       return false unless n1.neighbors.size == n2.neighbors.size
@@ -27,6 +27,6 @@ def self.are_equals(n1, n2)
       return true
     end
 
-    n1.nil? && n2.nil?
+    !n1 && !n2
   end
 end