Update 0019.删除链表的倒数第N个节点.md，修复 CPP 解法代码中的内存泄漏

problems/0019.删除链表的倒数第N个节点.md

@@ -75,7 +75,11 @@ public:
             fast = fast->next;
             slow = slow->next;
         }
-        slow->next = slow->next->next;
+        
+        ListNode *nth = slow->next;
+        slow->next = nth->next;
+        delete nth;
+        
         return dummyHead->next;
     }
 };