Fix inconsistent comments Ruby - chapter array and linked list (#1202)

* fix: inconsistent comments Ruby - chapter array and linked list

* fix: better Ruby code & comments

codes/ruby/utils/list_node.rb

@@ -9,8 +9,8 @@ class ListNode
   attr_accessor :val  # 节点值
   attr_accessor :next # 指向下一节点的引用
 
-  def initialize(val=nil, next_node=nil)
-    @val = val || 0
+  def initialize(val=0, next_node=nil)
+    @val = val
     @next = next_node
   end
 end

docs/chapter_array_and_linkedlist/linked_list.md

@@ -178,8 +178,8 @@
       attr_accessor :val  # 节点值
       attr_accessor :next # 指向下一节点的引用
 
-      def initialize(val=nil, next_node=nil)
-        @val = val || 0
+      def initialize(val=0, next_node=nil)
+        @val = val
         @next = next_node
       end
     end
@@ -709,8 +709,8 @@
       attr_accessor :next   # 指向后继节点的引用
       attr_accessor :prev   # 指向前驱节点的引用
 
-      def initialize(val=nil, next_node=nil, prev_node=nil)
-        @val = val || 0
+      def initialize(val=0, next_node=nil, prev_node=nil)
+        @val = val
         @next = next_node
         @prev = prev_node
       end

docs/chapter_array_and_linkedlist/list.md

@@ -282,9 +282,9 @@
 
     ```ruby title="list.rb"
     # 访问元素
-    num = nums[1]
+    num = nums[1] # 访问索引 1 处的元素
     # 更新元素
-    nums[1] = 0
+    nums[1] = 0 # 将索引 1 处的元素更新为 0
     ```
 
 === "Zig"
@@ -545,10 +545,10 @@
     nums << 4
 
     # 在中间插入元素
-    nums.insert 3, 6
+    nums.insert 3, 6 # 在索引 3 处插入数字 6
 
     # 删除元素
-    nums.delete_at 3
+    nums.delete_at 3 # 删除索引 3 处的元素
     ```
 
 === "Zig"
@@ -1005,7 +1005,7 @@
 
     ```ruby title="list.rb"
     # 排序列表
-    nums = nums.sort { |a, b| a <=> b }
+    nums = nums.sort { |a, b| a <=> b } # 排序后，列表元素从小到大排列
     ```
 
 === "Zig"