[fix/docs]: remove memory leak in queue (#2417)

* fix: remove memory leak in queue

* updating DIRECTORY.md

* clang-format and clang-tidy fixes for effd74c9

* style: simplify logic while using reserve

* style: use value_type as return type in front

* style: use proper error message

* style: use pre-increment and pre-decrement

* docs: use doxygen syntax

* docs: improve wording

Co-authored-by: github-actions[bot] <github-actions@users.noreply.github.com>
Co-authored-by: David Leal <halfpacho@gmail.com>

data_structures/queue.hpp

@@ -0,0 +1,104 @@
+/* This class specifies the basic operation on a queue as a linked list */
+#ifndef DATA_STRUCTURES_QUEUE_HPP_
+#define DATA_STRUCTURES_QUEUE_HPP_
+
+#include "node.hpp"
+
+/** Definition of the queue class */
+template <class ValueType>
+class queue {
+    using node_type = Node<ValueType>;
+
+ public:
+    using value_type = ValueType;
+    /**
+     * @brief prints the queue into the std::cout
+     */
+    void display() const {
+        std::cout << "Front --> ";
+        display_all(this->queueFront.get());
+        std::cout << '\n';
+        std::cout << "Size of queue: " << size << '\n';
+    }
+
+    /**
+     * @brief converts the queue into the std::vector
+     * @return std::vector containning all of the elements of the queue in the
+     * same order
+     */
+    std::vector<value_type> toVector() const {
+        return push_all_to_vector(this->queueFront.get(), this->size);
+    }
+
+ private:
+    /**
+     * @brief throws an exception if queue is empty
+     * @exception std::invalid_argument if queue is empty
+     */
+    void ensureNotEmpty() const {
+        if (isEmptyQueue()) {
+            throw std::invalid_argument("Queue is empty.");
+        }
+    }
+
+ public:
+    /**
+     * @brief checks if the queue has no elements
+     * @return true if the queue is empty, false otherwise
+     */
+    bool isEmptyQueue() const { return (queueFront == nullptr); }
+
+    /**
+     * @brief inserts a new item into the queue
+     */
+    void enQueue(const value_type& item) {
+        auto newNode = std::make_shared<node_type>();
+        newNode->data = item;
+        newNode->next = nullptr;
+        if (isEmptyQueue()) {
+            queueFront = newNode;
+            queueRear = newNode;
+        } else {
+            queueRear->next = newNode;
+            queueRear = queueRear->next;
+        }
+        ++size;
+    }
+
+    /**
+     * @return the first element of the queue
+     * @exception std::invalid_argument if queue is empty
+     */
+    value_type front() const {
+        ensureNotEmpty();
+        return queueFront->data;
+    }
+
+    /**
+     * @brief removes the first element from the queue
+     * @exception std::invalid_argument if queue is empty
+     */
+    void deQueue() {
+        ensureNotEmpty();
+        queueFront = queueFront->next;
+        --size;
+    }
+
+    /**
+     * @brief removes all elements from the queue
+     */
+    void clear() {
+        queueFront = nullptr;
+        queueRear = nullptr;
+        size = 0;
+    }
+
+ private:
+    std::shared_ptr<node_type> queueFront =
+        {}; /**< Pointer to the front of the queue */
+    std::shared_ptr<node_type> queueRear =
+        {}; /**< Pointer to the rear of the queue  */
+    std::size_t size = 0;
+};
+
+#endif  // DATA_STRUCTURES_QUEUE_HPP_