diff --git a/problems/0116.填充每个节点的下一个右侧节点指针.md b/problems/0116.填充每个节点的下一个右侧节点指针.md
index 003ef75a..60ea9210 100644
--- a/problems/0116.填充每个节点的下一个右侧节点指针.md
+++ b/problems/0116.填充每个节点的下一个右侧节点指针.md
@@ -358,7 +358,84 @@ function connect(root: NodePro | null): NodePro | null {
 };
 ```
 
+```csharp
+//递归
+public class Solution {
+    public Node Connect(Node root) {
+        if (root == null) {
+            return null;
+        }
+        
+        ConnectNodes(root.left, root.right);
+        
+        return root;
+    }
 
+    private void ConnectNodes(Node node1, Node node2) {
+        if (node1 == null || node2 == null) {
+            return;
+        }
+
+        // 将左子节点的 next 指向右子节点
+        node1.next = node2;
+
+        // 递归连接当前节点的左右子节点
+        ConnectNodes(node1.left, node1.right);
+        ConnectNodes(node2.left, node2.right);
+
+        // 连接跨越父节点的两个子树
+        ConnectNodes(node1.right, node2.left);
+    }
+}
+
+
+// 迭代
+public class Solution
+{
+    public Node Connect(Node root)
+    {
+        Queue<Node> que = new Queue<Node>();
+
+        if (root != null)
+        {
+            que.Enqueue(root);
+        }
+
+        while (que.Count > 0)
+        {
+
+            var queSize = que.Count;
+            for (int i = 0; i < queSize; i++)
+            {
+                var cur = que.Dequeue();
+
+                // 当这个节点不是这一层的最后的节点
+                if (i != queSize - 1)
+                {
+                    // 当前节点指向下一个节点
+                    cur.next = que.Peek();
+                }
+                // 否则指向空
+                else
+                {
+                    cur.next = null;
+                }
+
+                if (cur.left != null)
+                {
+                    que.Enqueue(cur.left);
+                }
+                if (cur.right != null)
+                {
+                    que.Enqueue(cur.right);
+                }
+            }
+        }
+
+        return root;
+    }
+}
+```
 
 
 <p align="center">
diff --git a/problems/0225.用队列实现栈.md b/problems/0225.用队列实现栈.md
index d89bf44b..6900e668 100644
--- a/problems/0225.用队列实现栈.md
+++ b/problems/0225.用队列实现栈.md
@@ -1046,6 +1046,8 @@ class MyStack() {
 
 ### C#:
 
+> 双队列
+
 ```csharp
 public class MyStack {
     Queue<int> queue1;
@@ -1080,6 +1082,54 @@ public class MyStack {
 }
 ```
 
+> 单队列
+
+```c#
+/*
+ * @lc app=leetcode id=225 lang=csharp
+ * 版本二：单队列
+ * [225] Implement Stack using Queues
+ */
+
+// @lc code=start
+public class MyStack {
+    Queue<int> myQueue;
+    public MyStack() {
+        myQueue = new Queue<int>();
+    }
+    
+    public void Push(int x) {
+        myQueue.Enqueue(x);
+    }
+    
+    //使用一个队列实现
+    public int Pop() {
+        //一个队列在模拟栈弹出元素的时候只要将队列头部的元素（除了最后一个元素外） 重新添加到队列尾部，此时再去弹出元素就是栈的顺序了。
+        for (var i = 0; i < myQueue.Count-1; i++)
+        {
+            myQueue.Enqueue(myQueue.Dequeue());
+        }
+        return myQueue.Dequeue();
+    }
+
+    //复用Pop()的代码
+    public int Top() {
+        int res = Pop();
+        myQueue.Enqueue(res);
+        return res;
+    }
+    
+    public bool Empty() {
+        return (myQueue.Count == 0);
+    }
+}
+
+// @lc code=end
+
+```
+
+
+
 ### PHP:
 
 > 双队列
@@ -1203,3 +1253,4 @@ impl MyStack {
 <a href="https://programmercarl.com/other/kstar.html" target="_blank">
   <img src="../pics/网站星球宣传海报.jpg" width="1000"/>
 </a>
+
diff --git a/problems/二叉树理论基础.md b/problems/二叉树理论基础.md
index e2c6d83c..50d592a2 100644
--- a/problems/二叉树理论基础.md
+++ b/problems/二叉树理论基础.md
@@ -302,9 +302,19 @@ impl<T> TreeNode<T> {
         }
     }
 }
-```
 
+```
+```c#
+public class TreeNode
+{
+    public int val;
+    public TreeNode left;
+    public TreeNode right;
+    public TreeNode(int x) { val = x; }
+}
+```
 <p align="center">
 <a href="https://programmercarl.com/other/kstar.html" target="_blank">
   <img src="../pics/网站星球宣传海报.jpg" width="1000"/>
 </a>
+
diff --git a/problems/二叉树的递归遍历.md b/problems/二叉树的递归遍历.md
index 92a8341f..edd55aad 100644
--- a/problems/二叉树的递归遍历.md
+++ b/problems/二叉树的递归遍历.md
@@ -623,3 +623,4 @@ public void Traversal(TreeNode cur, IList<int> res)
 <a href="https://programmercarl.com/other/kstar.html" target="_blank">
   <img src="../pics/网站星球宣传海报.jpg" width="1000"/>
 </a>
+