Update addTwoNumbers.md

addTwoNumbers.md

@@ -13,3 +13,20 @@ Explanation: 342 + 465 = 807.
 ## 思路
 
 ## 代码
+```js
+/**
+ * Definition for singly-linked list.
+ * function ListNode(val) {
+ *     this.val = val;
+ *     this.next = null;
+ * }
+ */
+/**
+ * @param {ListNode} l1
+ * @param {ListNode} l2
+ * @return {ListNode}
+ */
+var addTwoNumbers = function(l1, l2) {
+    
+};
+```