Add destructors to the C++ codes.

docs/chapter_stack_and_queue/queue.md

@@ -330,6 +330,10 @@ comments: true
             rear = nullptr;
             queSize = 0;
         }
+        ~LinkedListQueue() {
+            delete front;
+            delete rear;
+        }
         /* 获取队列的长度 */
         int size() {
             return queSize;
@@ -784,6 +788,9 @@ comments: true
             cap = capacity;
             nums = new int[capacity];
         }
+        ~ArrayQueue() {
+            delete[] nums;
+        }
         /* 获取队列的容量 */
         int capacity() {
             return cap;

docs/chapter_stack_and_queue/stack.md

@@ -324,6 +324,9 @@ comments: true
             stackTop = nullptr;
             stkSize = 0;
         }
+        ~LinkedListStack() {
+            freeMemoryLinkedList(stackTop);
+        }
         /* 获取栈的长度 */
         int size() {
             return stkSize;