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 2533a618..b6d08dbe 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
@@ -153,23 +153,27 @@ public:
 递归
 ```java
 class Solution {
-    TreeNode pre;// 记录上一个遍历的结点
+    TreeNode pre; // 记录上一个遍历的结点
     int result = Integer.MAX_VALUE;
+
     public int getMinimumDifference(TreeNode root) {
-       if(root==null)return 0;
-       traversal(root);
-       return result;
+        if (root == null)
+            return 0;
+        traversal(root);
+        return result;
     }
-    public void traversal(TreeNode root){
-        if(root==null)return;
-        //左
+
+    public void traversal(TreeNode root) {
+        if (root == null)
+            return;
+        // 左
         traversal(root.left);
-        //中
-        if(pre!=null){
-            result = Math.min(result,root.val-pre.val);
+        // 中
+        if (pre != null) {
+            result = Math.min(result, root.val - pre.val);
         }
         pre = root;
-        //右
+        // 右
         traversal(root.right);
     }
 }
@@ -182,22 +186,27 @@ class Solution {
         TreeNode pre = null;
         int result = Integer.MAX_VALUE;
 
-        if(root != null)
+        if (root != null)
             stack.add(root);
-        while(!stack.isEmpty()){
+
+        // 中序遍历（左中右），由于栈先入后出，反序（右中左）
+        while (!stack.isEmpty()) {
             TreeNode curr = stack.peek();
-            if(curr != null){
+            if (curr != null) {
                 stack.pop();
-                if(curr.right != null)
+                // 右
+                if (curr.right != null)
                     stack.add(curr.right);
+                // 中（先用null标记）
                 stack.add(curr);
                 stack.add(null);
-                if(curr.left != null)
+                // 左
+                if (curr.left != null)
                     stack.add(curr.left);
-            }else{
+            } else { // 中（遇到null再处理）
                 stack.pop();
                 TreeNode temp = stack.pop();
-                if(pre != null)
+                if (pre != null)
                     result = Math.min(result, temp.val - pre.val);
                 pre = temp;
             }
@@ -674,3 +683,4 @@ public class Solution
 <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>
+