Stack queue in cpp (#936)

* adding c++ implementation of stack and queue

* improved some comments

* Update contents/stacks_and_queues/code/c++/queue.cpp

adding version T const& front() const

Co-authored-by: Dimitri Belopopsky <ShadowMitia@users.noreply.github.com>

* Update contents/stacks_and_queues/code/c++/queue.cpp

removing unnecessary comment

Co-authored-by: Dimitri Belopopsky <ShadowMitia@users.noreply.github.com>

* improved implementation

* fixed queue implementation

* renamed queue API push as enqueue

* Rename code folder to cpp

* Inline newlines

Co-authored-by: Dimitri Belopopsky <ShadowMitia@users.noreply.github.com>
Co-authored-by: Dimitri Belopopsky <dimitri@belopopsky.com>

Author: ishwar00

contents/stacks_and_queues/code/cpp/queue.cpp

@@ -0,0 +1,91 @@
+#include<iostream>
+#include<memory>
+#include<cassert>
+
+namespace my {
+    /**
+     * implementation using linked list
+     * [value][next] -> [value][next] -> ... -> [value][next]
+     *  (front Node)   (intermediat Nodes)     (rear Node)
+     */
+    template<typename T>
+    struct Node {
+        /**
+        * next: will store right Node address
+        */
+        T value;
+        std::shared_ptr<Node<T>> next;
+        Node(const T& V) : value(V) { }
+    };
+
+    template<typename T>
+    class queue {
+    private:
+        /**
+         * front_pointer:  points to left most node
+         * count: keeps track of current number of elements present in queue
+         * rear_pointer:  points to most recent Node added into the queue, which is right most Node
+         */
+        std::shared_ptr<Node<T>> front_pointer;
+        std::shared_ptr<Node<T>> rear_pointer;
+        size_t count;
+    public:
+        queue() : count(0ULL) { }
+
+        void enqueue(const T& element) {
+            auto new_node = std::make_shared<Node<T>>(element);
+            if (count > 0) {
+                rear_pointer->next = new_node;
+                rear_pointer = new_node;
+            } else {
+                rear_pointer = front_pointer = new_node;
+            }
+            count = count + 1;
+        }
+
+        void dequeue() {
+            if (count > 1) {
+                front_pointer = front_pointer->next;
+                count = count - 1;
+            } else if (count == 1) {
+                front_pointer.reset();
+                rear_pointer.reset();
+                count = count - 1;
+            }
+        }
+
+        T& front() {
+            assert(count > 0 && "calling front on an empty queue");
+            return front_pointer->value;
+        }
+
+        T const& front() const {
+            assert(count > 0 && "calling front on an empty queue");
+            return front_pointer->value;
+        }
+
+        size_t size() const { return count; }
+
+        bool empty() const { return count == 0; }
+
+        ~queue() {
+            while (front_pointer.get() != nullptr) {
+                front_pointer = front_pointer->next;
+            }
+        }
+    };
+}
+
+int main() {
+  my::queue<int> intQueue;
+  intQueue.enqueue(4);
+  intQueue.enqueue(5);
+  intQueue.enqueue(9);
+
+  int frontElement = intQueue.front();
+  intQueue.dequeue();
+  std::cout << frontElement << '\n';
+  std::cout << intQueue.size() << '\n';
+  std::cout << intQueue.front() << '\n';
+  return 0;
+}

contents/stacks_and_queues/code/cpp/stack.cpp

@@ -0,0 +1,84 @@
+#include<iostream>
+#include<cassert>
+#include<memory>
+
+namespace my {
+    /**
+     * implementation using linked list
+     * [value][next] -> [value][next] -> ... -> [value][next]
+     * (top Node)      (intermediat Nodes)
+     * left most Node represents top element of stack
+     */
+    template<typename T>
+    struct Node {
+        /**
+        * next: will store right Node address
+        */
+        T value;
+        std::unique_ptr<Node<T>> next;
+        Node(const T& V) : value(V) { }
+    };
+
+    template<typename T>
+    class stack {
+    private:
+        /**
+         * top_pointer: points to left most node
+         * count: keeps track of current number of elements present in stack
+         */
+        std::unique_ptr<Node<T>> top_pointer;
+        size_t count;
+    public:
+        stack() : count(0ULL) { }
+
+        void push(const T& element) {
+            auto new_node = std::make_unique<Node<T>>(element);
+            new_node->next = std::move(top_pointer);
+            top_pointer = std::move(new_node);
+            count = count + 1;
+        }
+
+        void pop() {
+            if (count > 0) {
+                top_pointer = std::move(top_pointer->next);
+                count = count - 1;
+            }
+        }
+
+        T& top() {
+            assert(count > 0 and "calling top() on an empty stack");
+            return top_pointer->value;
+        }
+        // returning mutable reference can very be usefull if someone wants to modify top element
+
+        T const& top() const {
+            assert(count > 0 and "calling top() on an empty stack");
+            return top_pointer->value;
+        }
+
+        size_t size() const { return count; }
+
+        bool empty() const { return count == 0; }
+
+        ~stack() {
+            while (top_pointer.get() != nullptr) {
+                top_pointer = std::move(top_pointer->next);
+            }
+        }
+    };
+}
+
+int main() {
+  my::stack<int> intStack;
+
+  intStack.push(4);
+  intStack.push(5);
+  intStack.push(9);
+
+  int topElement = intStack.top();
+  intStack.pop();
+  std::cout << topElement << '\n';
+  std::cout << intStack.size() << '\n';
+  std::cout << intStack.top() << '\n';
+  return 0;
+}

contents/stacks_and_queues/stacks_and_queues.md

@@ -19,6 +19,9 @@ Here is a simple implementation of a stack:
 {% sample lang="ts" %}
 [import, lang:"typescript"](code/typescript/stack.ts)
 {% sample lang="java" %}
+[import, lang:"java"](code/java/Stack.java)
+{% sample lang = "cpp"%}
+[import, lang:"cpp"](code/cpp/stack.cpp)
 [import, lang:"java"](code/java/StackTest.java)
 {% sample lang="rust" %}
 [import, lang:"rust"](code/rust/Stack.rs)
@@ -29,6 +32,9 @@ Here is a simple implementation of a queue:
 {% sample lang="ts" %}
 [import, lang:"typescript"](code/typescript/queue.ts)
 {% sample lang="java" %}
+[import, lang:"java" ](code/java/Queue.java)
+{% sample lang = "cpp"%}
+[import, lang:"cpp"](code/cpp/queue.cpp)
 [import, lang:"java" ](code/java/QueueTest.java)
 {% sample lang="rust" %}
 [import, lang:"rust" ](code/rust/Queue.rs)