list.cpp

// Program to Insert node at nth position in a linked list
// Time Complexity - O(N)

#include <iostream>
using namespace std;

struct Node
{
    //To store the element
    int data;
    //To store the address of next element
    Node *next;
};

//Pointer to head Node initialize to NULL
Node *head = NULL;
int size = 0;

void insertAtNthNode(int x, int n)
{
    if (n < 1 || n > size + 1)
    {
        cout << "Position is not valid.\n";
        return;
    }

    // Increase size
    ++size;

    //Extra space for new Node
    Node *temp = (Node *)malloc(sizeof(Node));

    //Store the value in the Node
    temp->data = x;

    //Initialize address as NULL
    temp->next = NULL;

    //If Insertion taking place at Beginning
    if (n == 1)
    {
        temp->next = head;
        head = temp; //It Point Head Node
        return;
    }

    //To connect link with (n-1)th Node
    Node *temp1 = head;

    //Iterate to get (n-1)th Node address
    for (int i = 0; i < n - 2; i++)
        temp1 = temp1->next;

    //Store new address
    temp->next = temp1->next;
    temp1->next = temp;
}

//Fxn to delete N'th Node
void Delete(int n)
{
    if (n < 1 || n > size + 1)
    {
        cout << "Position is not valid.\n";
        return;
    }

    // Decrease the Size
    --size;
    
    Node *temp1 = head;

    if (n == 1)
    {
        //Head node is deleted and
        //Now head is pointed to next element
        head = temp1->next;
        free(temp1);
        return;
    }

    for (int i = 0; i < n - 2; i++)
        temp1 = temp1->next;

    //Pointer who point to N'th node
    Node *temp2 = temp1->next;
    temp1->next = temp2->next;

    //delete N'th node
    free(temp2);
}

void Update(int x, int n)
{
    if (n < 1 || n > size + 1)
    {
        cout << "Position is not valid.\n";
        return;
    }

    Node* temp = head;
    
    // Iterate n-1 times
    while (--n)
        temp = temp->next;

    //Update its value
    temp->data = x;
}

//function to Reverse linked list
void Reverse()
{
    Node *current, *prev, *next;

    current = head;
    prev = NULL;

    while (current != NULL)
    {
        next = current->next;
        current->next = prev;
        prev = current;
        current = next;
    }
    head = prev;
}

void PrintList()
{
    //Initialize to Head Node
    Node *temp = head;

    cout << "\nList is : ";

    //Print until Last node
    while (temp != NULL)
    {
        cout << temp->data << " ";
        temp = temp->next;
    }

    cout << "\n";
}

int main()
{
    int n, x, op;
    while (true)
    {
        cout << "\n"
             << "Enter 1 for Insertion\n"
             << "2 for Delete a node\n"
             << "3 for Updating Value\n"
             << "4 for Priniting List\n"
             << "5 for Reverse given list\n"
             << "Any Number for Quit\n";
        cin >> op;

        if (op == 1)
        {
            cout << "Enter Number and its position : ";
            cin >> x >> n;
            insertAtNthNode(x, n);
        }
        else if (op == 2)
        {
            cout << "Enter the position of Node : ";
            cin >> n;
            Delete(n);
        }
        else if (op == 3)
        {
            cout << "Enter Number and its position : ";
            cin >> x >> n;
            Update(x, n);
        }
        else if (op == 4)
            PrintList();
        else if (op == 5)
            Reverse();
        else
            break;
    }

    return 0;
}