add c++ Templates data structure of Doubly Link List

Data_Structures/Linked_List/Doubly_Linked_List/DoublyLinkedList_C++_Template/DLL.h

@@ -0,0 +1,247 @@
+#include <iostream>
+
+/*
+Class DLList is Double Linked List without a sentinel node
+Class Sentinel is Double Linked List using a sentinel node
+If you want to know more about sentinel node, here is the explanation from Wikipedia
+https://en.wikipedia.org/wiki/Sentinel_node#:~:text=The%20list%20starts%20out%20with,previous%20pointers%20point%20to%20itself.&text=In%20a%20non%2Dempty%20list,the%20tail%20of%20the%20list.
+
+*/
+
+/* DLL Class without a sentinel node */
+template <typename T>
+class DLL {
+	struct Node {
+		T m_data;
+		Node* m_next;
+		Node* m_prev;
+		Node(const T& data = T{}, Node* next = nullptr, Node* prev = nullptr) {
+			m_data = data;
+			m_next = next;
+			m_prev = prev;
+		}
+	};
+	Node* m_front;
+	Node* m_back;
+public:
+	DLL() {
+		m_front = nullptr;
+		m_back = nullptr;
+	}
+	void push_front(const T& data);
+	void push_back(const T& data);
+	void pop_front();
+	void pop_back();
+	void print() const;
+	void reversePrint() const;
+	~DLL();
+};
+
+
+template <typename T>
+void DLL<T>::push_front(const T& data) {
+	Node* nn = new Node(data, m_front);
+	if (m_front != nullptr) {
+		m_front->m_prev = nn;
+	}
+	else {
+		m_back = nn;
+	}
+	m_front = nn;
+}
+
+
+template <typename T>
+void DLL<T>::push_back(const T& data) {
+	Node* nn = new Node(data, nullptr, m_back);
+	if (m_back != nullptr) {
+		m_back->m_next = nn;
+	}
+	else {
+		m_front = nn;
+	}
+	m_back = nn;
+}
+
+
+template <typename T>
+void DLL<T>::pop_front() {
+	if (m_front != nullptr) {
+		Node* rm = m_front;
+		m_front = rm->m_next;
+		if (m_front != nullptr) {
+			m_front->m_prev = nullptr;
+		}
+		else {
+			m_back = nullptr;
+		}
+		delete rm;
+	}
+
+}
+
+
+template <typename T>
+void DLL<T>::pop_back() {
+	if (m_back != nullptr) {
+		Node* rm = m_back;
+		m_back = rm->m_prev;
+		if (m_back != nullptr) {
+			m_back->m_next = nullptr;
+		}
+		else {
+			m_front = nullptr;
+		}
+		delete rm;
+	}
+
+}
+
+
+template <typename T>
+void DLL<T>::print() const {
+	Node* curr = m_front;
+	while (curr != nullptr) {
+		std::cout << curr->m_data << " ";
+		curr = curr->m_next;
+	}
+	if (!m_front) {
+		std::cout << "empty list";
+	}
+	std::cout << std::endl;
+}
+
+
+template <typename T>
+void DLL<T>::reversePrint() const {
+	Node* curr = m_back;
+	while (curr != nullptr) {
+		std::cout << curr->m_data << " ";
+		curr = curr->m_prev;
+	}
+	if (!m_back) {
+		std::cout << "empty list";
+	}
+	std::cout << std::endl;
+}
+
+
+template <typename T>
+DLL<T>::~DLL() {
+	while (m_front) {
+		Node* it = m_front;
+		m_front = it->m_next;
+		delete it;
+	}
+}
+
+/* Sentinel Class using a sentinel node */
+template <typename T>
+class Sentinel {
+	struct Node {
+		T m_data;
+		Node* m_next;
+		Node* m_prev;
+		Node(const T& data = T{}, Node* next = nullptr, Node* prev = nullptr) {
+			m_data = data;
+			m_next = next;
+			m_prev = prev;
+		}
+	};
+	Node* m_front;
+	Node* m_back;
+public:
+	Sentinel() {
+		m_front = new Node();
+		m_back = new Node();
+		m_front->m_next = m_back;
+		m_back->m_prev = m_front;
+	}
+	void push_front(const T& data);
+	void push_back(const T& data);
+	void pop_front();
+	void pop_back();
+	void print() const;
+	void reversePrint() const;
+	~Sentinel();
+};
+
+
+template <typename T>
+void Sentinel<T>::push_front(const T& data) {
+	Node* nn = new Node(data, m_front->m_next, m_front);
+	m_front->m_next->m_prev = nn;
+	m_front->m_next = nn;
+}
+
+
+template <typename T>
+void Sentinel<T>::push_back(const T& data) {
+	Node* nn = new Node(data, m_back, m_back->m_prev);
+	m_back->m_prev->m_next = nn;
+	m_back->m_prev = nn;
+}
+
+
+template <typename T>
+void Sentinel<T>::pop_front() {
+	//if its an empty list... note that it means
+	//front sentinel's next node is the back sentinel
+	if (m_front->m_next != m_back) {
+		Node* rm = m_front->m_next;
+		Node* B = rm->m_next;
+		m_front->m_next = B;
+		B->m_prev = m_front;
+		delete rm;
+	}
+}
+
+
+template <typename T>
+void Sentinel<T>::pop_back() {
+	if (m_back->m_prev != m_front) {
+		Node* rm = m_back->m_prev;
+		rm->m_prev->m_next = m_back;
+		m_back->m_prev = rm->m_prev;
+		delete rm;
+	}
+}
+
+
+template <typename T>
+void Sentinel<T>::print() const {
+	Node* curr = m_front->m_next;
+	while (curr != m_back) {
+		std::cout << curr->m_data << " ";
+		curr = curr->m_next;
+	}
+	if (m_front->m_next == m_back) {
+		std::cout << "empty list";
+	}
+	std::cout << std::endl;
+}
+
+
+template <typename T>
+void Sentinel<T>::reversePrint() const {
+	Node* curr = m_back->m_prev;
+	while (curr != m_front) {
+		std::cout << curr->m_data << " ";
+		curr = curr->m_prev;
+	}
+	if (m_back->m_prev == m_front) {
+		std::cout << "empty list";
+	}
+	std::cout << std::endl;
+}
+
+
+template <typename T>
+Sentinel<T>::~Sentinel() {
+	while (m_front != m_back) {
+		Node* it = m_front;
+		m_front = it->m_next;
+		delete it;
+	}
+}
+

Data_Structures/Linked_List/Doubly_Linked_List/DoublyLinkedList_C++_Template/DLLtest.cpp

@@ -0,0 +1,134 @@
+/* tester */
+
+#include "DLL.h"
+#include <iostream>
+
+int main(void) {
+	DLL<int> regular;
+	Sentinel<int> sentinel;
+
+	/* DLL class test */
+	std::cout << "testing regular doubly linked list" << std::endl;
+
+	// test push_front();
+	for (int i = 0; i < 3; i++) {
+		regular.push_front(i);
+		regular.print(); 				
+	}
+	regular.reversePrint();    
+
+	//test push_back();
+	for (int i = 3; i < 6; i++) {
+		regular.push_back(i);
+		regular.print();
+	}
+	regular.reversePrint();
+
+	//test pop_front() & pop_back()
+	for (int i = 0; i < 7; i++) {
+		if (i % 2 == 0) {
+			regular.pop_front();
+		}
+		else {
+			regular.pop_back();
+		}
+		regular.print();
+	}
+	regular.reversePrint();
+
+	//test push_back();
+	for (int i = 0; i < 3; i++) {
+		regular.push_back(i);
+		regular.print();
+	}
+	regular.reversePrint();
+
+
+	for (int i = 3; i < 6; i++) {
+		regular.push_front(i);
+		regular.print();
+	}
+	regular.reversePrint();
+
+	//test pop_front()
+	for (int i = 0; i < 7; i++) {
+		if (i % 2) {
+			regular.pop_front();
+		}
+		else {
+			regular.pop_back();
+		}
+		regular.print();
+	}
+	regular.reversePrint();
+
+
+	for (int i = 0; i < 3; i++) {
+		regular.push_front(i);
+		regular.print();
+	}
+	regular.reversePrint();
+
+
+	/* Sentinel class test */
+
+	std::cout << "testing sentinel list" << std::endl;
+
+	//test push_front()
+	for (int i = 0; i < 3; i++) {
+		sentinel.push_front(i);
+		sentinel.print();
+	}
+	sentinel.reversePrint();
+
+	//test push_back()
+	for (int i = 3; i < 6; i++) {
+		sentinel.push_back(i);
+		sentinel.print();
+	}
+	sentinel.reversePrint();
+
+	//test pop_front() & pup_back()
+	for (int i = 0; i < 7; i++) {
+		if (i % 2 == 0) {
+			sentinel.pop_front();
+		}
+		else {
+			sentinel.pop_back();
+		}
+		sentinel.print();
+	}
+	sentinel.reversePrint();
+
+	for (int i = 0; i < 3; i++) {
+		sentinel.push_back(i);
+		sentinel.print();
+	}
+	sentinel.reversePrint();
+
+	for (int i = 3; i < 6; i++) {
+		sentinel.push_front(i);
+		sentinel.print();
+	}
+	sentinel.reversePrint();
+
+	for (int i = 0; i < 7; i++) {
+		if (i % 2) {
+			sentinel.pop_front();
+		}
+		else {
+			sentinel.pop_back();
+		}
+		sentinel.print();
+	}
+	sentinel.reversePrint();
+
+	for (int i = 0; i < 3; i++) {
+		sentinel.push_front(i);
+		sentinel.print();
+	}
+	sentinel.reversePrint();
+
+
+	return 0;
+}