Free memory after removing

a node from a LinkedList or TreeNode.

codes/cpp/chapter_stack_and_queue/linkedlist_queue.cpp

@@ -50,7 +50,10 @@ public:
     int poll() {
         int num = peek();
         // 删除头结点
+        ListNode *tmp = front;
         front = front->next;
+        // 释放内存
+        delete tmp; 
         queSize--;
         return num;
     }

codes/cpp/chapter_stack_and_queue/linkedlist_stack.cpp

@@ -39,7 +39,10 @@ public:
     /* 出栈 */
     int pop() {
         int num = top();
+        ListNode *tmp = stackTop;
         stackTop = stackTop->next;
+        // 释放内存
+        delete tmp;
         stkSize--;
         return num;
     }