Updated Linked Lists - 5/10/2017 V4.0, C++ (gcc)

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//g++  5.4.0

#include <iostream>
using namespace std;

class Node {
public:
	int data;
	Node *next;

Node(int value, Node *nxt = 0) {
		data = value;
		next = nxt;
	}

Node() {
		data = 0;
		next = 0;
	}
};

class List {
private:
	Node *head, *tail;

public:
	List() {
		head = tail = 0;
	}

void Add2Head(int value) {
		Node *n = new Node(value, 0);
		if (head == 0) {
			head = tail = n;
		}
		else {
			n->next = head;
			head = n;
		}
	}

void Add2Tail(int value) {
		Node *n = new Node(value, 0);
		if (head == 0) {
			head = tail = n;
		}
		else {
			tail->next = n;
			tail = n;
		}
	}

int Count() {
		int s = 0;
		Node *n = head;
		while (n != 0) {
			s++;
			n = n->next;
		}
		return s;
	}

void Print() {
		int i = 0;
		Node *n = head;
		while (n != 0) {
			cout << i << ".    " << (n->data) << endl;
			n = n->next;
			i++;
		}
	}

void PrintInReverse() {
		Node *n;
		for (int i = (this->Count() - 1); i >= 0; i--) {
			n = head;
			for (int j = 0; j<i; j++) {
				n = n->next;
			}
			cout << i << ".    " << (n->data) << endl;
		}
	}

Node* operator[](int index) {
		Node *n = head;
		int i = 0;
		while (i<index) {
			n = n->next;
			i++;
		}
		return n;
	}

Node* Access(int index) {
		Node *n = head;
		int i = 0;
		while (i<index) {
			n = n->next;
			i++;
		}
		return n;
	}

void DeleteHead() {
		Node *temp = new Node();
		if (head == 0) {
			return;
		}
		else if (head == tail) {
			head = tail = 0;
		}
		else {
			temp = head->next;
			delete head;
			head = temp;
		}
	}

void DeleteTail() {
		if (head == 0) {
			return;
		}
		else if (head == tail) {
			delete head;
			head = tail = 0;
		}
		else {
			Node *n = this->Access(this->Count() - 2);
			n->next = 0;
			delete tail;
			tail = n;

/*
			Node *n=head;
			while (n->next!=tail) {
			n=n->next;
			}
			n->next=0;
			delete tail;
			tail=n;
			*/
		}
	}

void DeleteNodeAt(int index) {

Node *before = this->Access(index - 1);
		Node *after = this->Access(index + 1);
		before->next = after;
	}

void InsertNodeAt(int index, int value) {
		Node *before = this->Access(index - 1);
		Node *temp = this->Access(index);
		Node *n = new Node(value, temp);
		before->next = n;
	}

void SortList() {
		Node *n = new Node();
		for (int i = 0; i < this->Count(); i++) {
			for (int j = i; j < this->Count(); j++) {
				if (i == j) {
					continue;
				}
				else {
					if (this->Access(i)->data > this->Access(j)->data) {
						n->data = this->Access(i)->data;
						this->Access(i)->data = this->Access(j)->data;
						this->Access(j)->data = n->data;
					}
				}
			}
		}
	}

bool KeyExist(int key) {
		int i = 0;
		while (i < this->Count()) {
			if (this->Access(i)->data == key) {
				return true;
			}
			i++;
		}
		return false;
	}

int IndexOf(int key) {
		int i = 0;
		int index = -1;
		while (i < this->Count()) {
			if (this->Access(i)->data == key) {
				index = i;
				break;
			}
			i++;
		}
		return index;
	}

int LastIndexOf(int key) {
		int i = 0;
		int index = -1;
		while (i< this->Count()) {
			if (this->Access(i)->data == key) {
				index = i;
			}
			i++;
		}
		return index;
	}

int* IndicesOf(int key, int &length) {
		length = 0;
		int i = 0;
		while (i< this->Count()) {
			if (this->Access(i)->data == key) {
				length++;
			}
			i++;
		}
		int *indices = new int[length];
		int index = 0;
		i = 0;
		while (i< this->Count()) {
			if (this->Access(i)->data == key) {
				indices[index] = i;
				index++;
			}
			i++;
		}
		return indices;
	}

bool IsSorted() {
		int i = 0;
		bool __IsSorted = true;
		while (i < this->Count() - 1) {
			if (!(this->Access(i)->data <= this->Access(i + 1)->data)) {
				__IsSorted = false;
				break;
			}
			i++;
		}
		return __IsSorted;
	}

void InsertNodeInSortedList(int value) {
		int i = 0;
		int index = 0;
		if (this->IsSorted()) {
			while (i < this->Count()) {
				if (this->Access(i)->data <= value) {
					index++;
				}
				i++;
			}
			this->InsertNodeAt(index, value);
		}
		else {
			this->SortList();
			while (i < this->Count()) {
				if (this->Access(i)->data <= value) {
					index++;
				}
				i++;
			}
			this->InsertNodeAt(index, value);
		}
	}

void DeleteNodeByKey(int value) {
		int i = 0;
		while (i < this->Count()) {
			if (this->Access(i)->data == value) {
				this->DeleteNodeAt(i);
			}
			i++;
		}
	}

/*
	~List() {

Node *temp = head;
		while (temp != 0) {
			delete temp;
			temp = temp->next;
		}
		delete temp;
		head = tail = 0;

}
	*/
};

int main()
{
	/*
		9	5
		10	8
		5	9
		9	9
		8	10
	*/

List l;
	l.Add2Head(9);
	l.Add2Head(5);
	l.Add2Head(10);
	l.Add2Head(9);
	l.Add2Tail(8);
	//l.SortList();
	l.InsertNodeInSortedList(7);

for (int i = 0; i < l.Count(); i++) {
		cout << (l[i])->data << "\t" << (l[i])->next << endl;
	}
	cout << "--------------------------" << endl;
	l.DeleteNodeByKey(9);

for (int i = 0; i < l.Count(); i++) {
		cout << (l[i])->data << "\t" << (l[i])->next << endl;
	}
	
	//system("pause");
}

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Compilation time: 0.32 sec, absolute running time: 0.12 sec, cpu time: 0.07 sec, memory peak: 3 Mb, absolute service time: 0,45 sec