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 8c47b633..bc9645dc 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
@@ -547,31 +547,25 @@ impl Solution {
 递归中解决
 
 ```rust
-static mut PRE: Option<i32> = None;
-static mut MIN: i32 = i32::MAX;
-
 impl Solution {
     pub fn get_minimum_difference(root: Option<Rc<RefCell<TreeNode>>>) -> i32 {
-        unsafe {
-            PRE = None;
-            MIN = i32::MAX;
-            Self::inorder(root);
-            MIN
-        }
+        let mut pre = None;
+        let mut min = i32::MAX;
+        Self::inorder(root, &mut pre, &mut min);
+        min
     }
-    pub fn inorder(root: Option<Rc<RefCell<TreeNode>>>) {
+    pub fn inorder(root: Option<Rc<RefCell<TreeNode>>>, pre: &mut Option<i32>, min: &mut i32) {
         if root.is_none() {
             return;
         }
         let node = root.as_ref().unwrap().borrow();
-        Self::inorder(node.left.clone());
-        unsafe {
-            if let Some(pre) = PRE {
-                MIN = (node.val - pre).min(MIN).abs();
-            }
-            PRE = Some(node.val)
+        Self::inorder(node.left.clone(), pre, min);
+        if let Some(pre) = pre {
+            *min = (node.val - *pre).min(*min);
         }
-        Self::inorder(node.right.clone());
+        *pre = Some(node.val);
+
+        Self::inorder(node.right.clone(), pre, min);
     }
 }
 ```