Update 0617.合并二叉树.md

problems/0617.合并二叉树.md

@@ -721,6 +721,49 @@ impl Solution {
 }
 ```
 
+迭代：
+
+```rust
+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 mut stack = vec![];
+        stack.push(root2);
+        stack.push(root1.clone());
+        while !stack.is_empty() {
+            let node1 = stack.pop().unwrap().unwrap();
+            let node2 = stack.pop().unwrap().unwrap();
+            let mut node1 = node1.borrow_mut();
+            let node2 = node2.borrow();
+            node1.val += node2.val;
+            if node1.left.is_some() && node2.left.is_some() {
+                stack.push(node2.left.clone());
+                stack.push(node1.left.clone());
+            }
+            if node1.right.is_some() && node2.right.is_some() {
+                stack.push(node2.right.clone());
+                stack.push(node1.right.clone());
+            }
+            if node1.left.is_none() && node2.left.is_some() {
+                node1.left = node2.left.clone();
+            }
+            if node1.right.is_none() && node2.right.is_some() {
+                node1.right = node2.right.clone();
+            }
+        }
+        root1
+    }
+}
+```
+
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