Update 530.二叉搜索树的最小绝对差，添加C#版

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);
+    }
+}
+```
 
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