diff --git a/problems/0098.验证二叉搜索树.md b/problems/0098.验证二叉搜索树.md
index 184060a5..319ad1aa 100644
--- a/problems/0098.验证二叉搜索树.md
+++ b/problems/0098.验证二叉搜索树.md
@@ -791,6 +791,20 @@ impl Solution {
     }
 }
 ```
+### C#
+```C#
+// 递归
+public long val = Int64.MinValue;
+public bool IsValidBST(TreeNode root)
+{
+    if (root == null) return true;
+    bool left = IsValidBST(root.left);
+    if (root.val > val) val = root.val;
+    else return false;
+    bool right = IsValidBST(root.right);
+    return left && right;
+}
+```
 
 <p align="center">
 <a href="https://programmercarl.com/other/kstar.html" target="_blank">
diff --git a/problems/0530.二叉搜索树的最小绝对差.md b/problems/0530.二叉搜索树的最小绝对差.md
index 56911858..f08df577 100644
--- a/problems/0530.二叉搜索树的最小绝对差.md
+++ b/problems/0530.二叉搜索树的最小绝对差.md
@@ -647,6 +647,27 @@ impl Solution {
     }
 }
 ```
+### C#
+```C#
+// 递归
+public class Solution
+{
+    public List<int> res = new List<int>();
+    public int GetMinimumDifference(TreeNode root)
+    {
+        Traversal(root);
+        return res.SelectMany((x, i) => res.Skip(i + 1).Select(y => Math.Abs(x - y))).Min();
+
+    }
+    public void Traversal(TreeNode root)
+    {
+        if (root == null) return;
+        Traversal(root.left);
+        res.Add(root.val);
+        Traversal(root.right);
+    }
+}
+```
 
 <p align="center">
 <a href="https://programmercarl.com/other/kstar.html" target="_blank">
diff --git a/problems/0700.二叉搜索树中的搜索.md b/problems/0700.二叉搜索树中的搜索.md
index bc21bab8..65e69219 100644
--- a/problems/0700.二叉搜索树中的搜索.md
+++ b/problems/0700.二叉搜索树中的搜索.md
@@ -464,6 +464,28 @@ impl Solution {
     }
 }
 ```
+### C#
+```C#
+// 递归
+public TreeNode SearchBST(TreeNode root, int val)
+{
+    if (root == null || root.val == val) return root;
+    if (root.val > val) return SearchBST(root.left, val);
+    if (root.val < val) return SearchBST(root.right, val);
+    return null;
+}
+//  迭代
+public TreeNode SearchBST(TreeNode root, int val)
+{
+    while (root != null)
+    {
+        if (root.val > val) root = root.left;
+        else if (root.val < val) root = root.right;
+        else return root;
+    }
+    return null;
+}
+```
 
 <p align="center">
 <a href="https://programmercarl.com/other/kstar.html" target="_blank">