JavaScript版本的合并二叉树

problems/0617.合并二叉树.md

@@ -370,6 +370,36 @@ func mergeTrees(t1 *TreeNode, t2 *TreeNode) *TreeNode {
 }
 ```
 
+JavaScript:
+
+```javascript
+/**
+ * Definition for a binary tree node.
+ * function TreeNode(val, left, right) {
+ *     this.val = (val===undefined ? 0 : val)
+ *     this.left = (left===undefined ? null : left)
+ *     this.right = (right===undefined ? null : right)
+ * }
+ */
+/**
+ * @param {TreeNode} root1
+ * @param {TreeNode} root2
+ * @return {TreeNode}
+ */
+var mergeTrees = function (root1, root2) {
+    const preOrder = (root1, root2) => {
+        if (!root1)
+            return root2
+        if (!root2)
+            return root1;
+        root1.val += root2.val;
+        root1.left = preOrder(root1.left, root2.left);
+        root1.right = preOrder(root1.right, root2.right);
+        return root1;
+    }
+    return preOrder(root1, root2);
+};
+```
 
 
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