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

@@ -396,6 +396,30 @@ impl Solution {
 }
 ```
 
+迭代：
+
+```rust
+impl Solution {
+    pub fn convert_bst(root: Option<Rc<RefCell<TreeNode>>>) -> Option<Rc<RefCell<TreeNode>>> {
+        let mut cur = root.clone();
+        let mut stack = vec![];
+        let mut pre = 0;
+        while !stack.is_empty() || cur.is_some() {
+            while let Some(node) = cur {
+                cur = node.borrow().right.clone();
+                stack.push(node);
+            }
+            if let Some(node) = stack.pop() {
+                pre += node.borrow().val;
+                node.borrow_mut().val = pre;
+                cur = node.borrow().left.clone();
+            }
+        }
+        root
+    }
+}
+```
+
 
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