Update 0024.两两交换链表中的节点.md

添加javascript递归版本实现

problems/0024.两两交换链表中的节点.md

@@ -285,6 +285,21 @@ var swapPairs = function (head) {
 };
 ```
 
+```javascript
+// 递归版本
+var swapPairs = function (head) {
+  if (head == null || head.next == null) {
+    return head;
+  }
+
+  let after = head.next;
+  head.next = swapPairs(after.next);
+  after.next = head;
+
+  return after;
+};
+```
+
 ### TypeScript：
 
 ```typescript