Update 0530.二叉搜索树的最小绝对差.md

problems/0530.二叉搜索树的最小绝对差.md

@@ -544,6 +544,38 @@ 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
+        }
+    }
+    pub fn inorder(root: Option<Rc<RefCell<TreeNode>>>) {
+        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.right.clone());
+    }
+}
+```
+
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