Update 0538.把二叉搜索树转换为累加树.md

problems/0538.把二叉搜索树转换为累加树.md

@@ -371,6 +371,31 @@ object Solution {
 }
 ```
 
+## rust
+
+递归：
+
+```rust
+impl Solution {
+    pub fn convert_bst(root: Option<Rc<RefCell<TreeNode>>>) -> Option<Rc<RefCell<TreeNode>>> {
+        let mut pre = 0;
+        Self::traversal(&root, &mut pre);
+        root
+    }
+
+    pub fn traversal(cur: &Option<Rc<RefCell<TreeNode>>>, pre: &mut i32) {
+        if cur.is_none() {
+            return;
+        }
+        let mut node = cur.as_ref().unwrap().borrow_mut();
+        Self::traversal(&node.right, pre);
+        *pre += node.val;
+        node.val = *pre;
+        Self::traversal(&node.left, pre);
+    }
+}
+```
+
 
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