Update 0617.合并二叉树.md

problems/0617.合并二叉树.md

@@ -691,6 +691,35 @@ object Solution {
 }
 ```
 
+### rust
+
+递归：
+
+```rust
+use std::cell::RefCell;
+use std::rc::Rc;
+impl Solution {
+    pub fn merge_trees(
+        root1: Option<Rc<RefCell<TreeNode>>>,
+        root2: Option<Rc<RefCell<TreeNode>>>,
+    ) -> Option<Rc<RefCell<TreeNode>>> {
+        if root1.is_none() {
+            return root2;
+        }
+        if root2.is_none() {
+            return root1;
+        }
+        let binding = root1.clone();
+        let mut node1 = binding.as_ref().unwrap().borrow_mut();
+        let node2 = root2.as_ref().unwrap().borrow_mut();
+        node1.left = Self::merge_trees(node1.left.clone(), node2.left.clone());
+        node1.right = Self::merge_trees(node1.right.clone(), node2.right.clone());
+        node1.val += node2.val;
+
+        root1
+    }
+}
+```
 
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