From 0661f09ae85bcdd59d45b7a5ec1010fe39025437 Mon Sep 17 00:00:00 2001
From: Adarsh Kishore <76656932+adarsh-kishore786@users.noreply.github.com>
Date: Tue, 14 Sep 2021 19:15:07 +0530
Subject: [PATCH] chore(CPlusPlus): add linked list implementation (#463)

---
 algorithms/CPlusPlus/Linked-Lists/singly.cpp | 158 ++++++++++++++++---
 1 file changed, 134 insertions(+), 24 deletions(-)

diff --git a/algorithms/CPlusPlus/Linked-Lists/singly.cpp b/algorithms/CPlusPlus/Linked-Lists/singly.cpp
index 178cc7e7..34bd698e 100644
--- a/algorithms/CPlusPlus/Linked-Lists/singly.cpp
+++ b/algorithms/CPlusPlus/Linked-Lists/singly.cpp
@@ -1,19 +1,23 @@
 #include <iostream>
+#include <exception>
 
-template <typename T>
-class Node {
-    public:
-        T data;
-        Node *next;
+using dType = int;
 
-        Node(T data)
-            : data(data) , next(nullptr) {};
-        Node(){}
-};
 
 template <typename T>
 class SinglyLinkedList {
     private:
+        template <typename N>
+        class Node {
+            public:
+                T data;
+                Node *next;
+
+                Node(T data)
+                    : data(data) , next(nullptr) {};
+                Node(){}
+        };
+
         Node<T>* head;
         Node<T>* tail;
 
@@ -21,6 +25,19 @@ class SinglyLinkedList {
         SinglyLinkedList()
             : head(nullptr),tail(nullptr){}
 
+        ~SinglyLinkedList(){
+            Node<T> *itr = this->head;
+            // iterate through list until itr reach to nullptr and print data
+            while(itr != nullptr) {
+                // creating temporary pointer to delete memory
+                Node<T> *temp_ptr = itr;
+                itr = itr->next;
+                delete temp_ptr;
+            }
+
+            // std::cout << "Destructor called\n";
+        }
+
         void insertAtHead(T data) {
             Node<T> *temp = new Node<T>(data);
 
@@ -36,7 +53,7 @@ class SinglyLinkedList {
             // change head point to new node
             this->head = temp;
         }
-    
+
         void insertAtEnd(T data){
 
             Node<T> *newNode = new Node<T>(data);
@@ -57,10 +74,8 @@ class SinglyLinkedList {
 
         T removeAtHead() {
             // if list is empty we can't remove node
-            if(this->head == nullptr) {
-                std::cout<<"List is Empty"<<std::endl;
-                exit(1);
-            }
+            if(this->head == nullptr)
+                throw std::runtime_error("List is Empty.");
 
             // save data of node where head is pointed
             T data = this->head->data;
@@ -73,9 +88,59 @@ class SinglyLinkedList {
             return data;
         }
 
+        T removeAtEnd() {
+            // if list is empty we can't remove node
+            if (this->head == nullptr)
+                throw std::runtime_error("List is Empty.");
+            // if list is singleton it just becomes nullptr
+            if(this->head->next == nullptr) {
+                T data = this->tail->data;
+
+                Node<T>* temp_ptr = this->tail;
+                this->head = nullptr;
+                this->tail = nullptr;
+
+                delete temp_ptr;
+                return data;
+            }
+
+            // save data of node where tail is pointed
+            T data = this->tail->data;
+
+            // now iterate to one before last pointer
+            Node<T>* currNode = this->head;
+            Node<T>* nextNode = currNode->next;
+
+            while (nextNode && nextNode->next)
+            {
+                currNode = nextNode;
+                nextNode = nextNode->next;
+            }
+
+            // save temp pointer to free the memory
+            Node<T>* temp_ptr = this->tail;
+            currNode->next = nullptr;
+            this->tail = currNode;
+
+            delete temp_ptr;
+            return data;
+        }
+
+        T front() {
+            if(this->head == nullptr)
+                throw std::runtime_error("Empty List.");
+            return this->head->data;
+        }
+
+        T back() {
+            if(this->head == nullptr)
+                throw std::runtime_error("Empty List.");
+            return this->tail->data;
+        }
+
         void printList() const {
             if(this->head == nullptr) {
-                std::cout<<"List is Empty"<<std::endl;
+                std::cout<<"List is Empty."<<std::endl;
             } else {
                 Node<T> *itr = this->head;
                 // iterate through list until itr reach to nullptr and print data
@@ -88,13 +153,58 @@ class SinglyLinkedList {
         }
 };
 
-int main() {
-    SinglyLinkedList<int> l;
-    l.insertAtHead(1);
-    l.insertAtHead(2);
-    l.insertAtHead(3);
-    l.insertAtEnd(5);
-    l.removeAtHead();
-    l.printList();
-    return 0;
+template <typename T>
+void insert_element(SinglyLinkedList<T>& list, bool front) {
+    T val {};
+    std::cout << "Enter value to be inserted: ";
+    std::cin >> val;
+
+    if (front) list.insertAtHead(val);
+    else list.insertAtEnd(val);
+}
+
+void menu() {
+    SinglyLinkedList<dType> list {};
+    while (true) {
+        std::cout << "\nWhat would you like to do?\n";
+        std::cout << "1. Push back an element\n";
+        std::cout << "2. Push front an element\n";
+        std::cout << "3. Display the linked list\n";
+        std::cout << "4. Get front\n";
+        std::cout << "5. Get back\n";
+        std::cout << "6. Pop front\n";
+        std::cout << "7. Pop back\n";
+        std::cout << "8. Quit\n";
+        std::cout << "Enter corresponding number to your choice: ";
+        int ch {};
+        std::cin >> ch;
+
+        try {
+            switch (ch) {
+                case 1: insert_element(list, false);
+                          break;
+                case 2: insert_element(list, true);
+                          break;
+                case 3: list.printList();
+                          break;
+                case 4: std::cout << list.front() << "\n";
+                          break;
+                case 5: std::cout << list.back() << "\n";
+                          break;
+                case 6: list.removeAtHead();
+                          break;
+                case 7: list.removeAtEnd();
+                          break;
+                case 8: return;
+                default: std::cout << "That's an invalid option. Please try again.\n";
+            }
+        }
+        catch (const std::runtime_error& re) {
+            std::cerr << re.what() << "\n";
+        }
+    }
+}
+
+int main() {
+    menu();
 }