update 二叉树的递归遍历.md about rust

problems/二叉树的递归遍历.md

@@ -525,6 +525,46 @@ object Solution {
   }
 }
 ```
+
+rust:
+
+```rust
+use std::cell::RefCell;
+use std::rc::Rc;
+impl Solution {
+    pub fn preorder_traversal(root: Option<Rc<RefCell<TreeNode>>>) -> Vec<i32> {
+        let mut res = vec![];
+        Self::traverse(&root, &mut res);
+        res
+    }
+
+//前序遍历
+    pub fn traverse(root: &Option<Rc<RefCell<TreeNode>>>, res: &mut Vec<i32>) {
+        if let Some(node) = root {
+            res.push(node.borrow().val);
+            Self::traverse(&node.borrow().left, res);
+            Self::traverse(&node.borrow().right, res);
+        }
+    }
+//后序遍历
+    pub fn traverse(root: &Option<Rc<RefCell<TreeNode>>>, res: &mut Vec<i32>) {
+        if let Some(node) = root {
+            Self::traverse(&node.borrow().left, res);
+            Self::traverse(&node.borrow().right, res);
+            res.push(node.borrow().val);
+        }
+    }
+//中序遍历
+    pub fn traverse(root: &Option<Rc<RefCell<TreeNode>>>, res: &mut Vec<i32>) {
+        if let Some(node) = root {
+            Self::traverse(&node.borrow().left, res);
+            res.push(node.borrow().val);
+            Self::traverse(&node.borrow().right, res);
+        }
+    }
+}
+```
+
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