seer/tests/hellocirlelist/hellocirclelist.cpp

#include<iostream>

// https://www.softwaretestinghelp.com/circular-linked-list/

using namespace std;

struct Node
{
    int data;
    struct Node *next;
};

//insert a new node in an empty list
struct Node *insertInEmpty(struct Node *last, int new_data)
{
    // if last is not null then list is not empty, so return
    if (last != NULL)
        return last;

    // allocate memory for node
    struct Node *temp = new Node;

    // Assign the data.
    temp -> data = new_data;
    last = temp;

    // Create the link.
    last->next = last;

    return last;
}

//insert new node at the beginning of the list
struct Node *insertAtBegin(struct Node *last, int new_data)
{
    //if list is empty then add the node by calling insertInEmpty
    if (last == NULL)
        return insertInEmpty(last, new_data);

    //else create a new node
    struct Node *temp = new Node;

    //set new data to node
    temp -> data = new_data;
    temp -> next = last -> next;
    last -> next = temp;

    return last;
}

//insert new node at the end of the list
struct Node *insertAtEnd(struct Node *last, int new_data)
{
    //if list is empty then add the node by calling insertInEmpty
    if (last == NULL)
        return insertInEmpty(last, new_data);

    //else create a new node
    struct Node *temp = new Node;

    //assign data to new node
    temp -> data = new_data;
    temp -> next = last -> next;
    last -> next = temp;
    last = temp;

    return last;
}

//insert a new node in between the nodes
struct Node *insertAfter(struct Node *last, int new_data, int after_item)
{
    //return null if list is empty
    if (last == NULL)
        return NULL;

    struct Node *temp, *p;
    p = last -> next;
    do
    {
        if (p ->data == after_item)
        {
            temp = new Node;
            temp -> data = new_data;
            temp -> next = p -> next;
            p -> next = temp;

            if (p == last)
                last = temp;
            return last;
        }
        p = p -> next;
    } while(p != last -> next);

    cout << "The node with data "<<after_item << " is not present in the list." << endl;
    return last;

}

//traverse the circular linked list
void traverseList(struct Node *last) {
    struct Node *p;

    // If list is empty, return.
    if (last == NULL) {
        cout << "Circular linked List is empty." << endl;
        return;
    }
    p = last -> next; // Point to the first Node in the list.

    // Traverse the list starting from first node until first node is visited again

    do {
        cout << p -> data << "==>";
        p = p -> next;
    } while(p != last->next);
    if(p == last->next)
        cout<<p->data;
    cout<<"\n\n";
}

//delete the node from the list
void deleteNode(Node** head, int key)
{
    // If linked list is empty retun
    if (*head == NULL)
        return;

    // If the list contains only a single node,delete that node; list is empty
    if((*head)->data==key && (*head)->next==*head) {
        free(*head);
        *head=NULL;
    }
    Node *last=*head,*d;

    // If key is the head
    if((*head)->data==key) {
        while(last->next!=*head) // Find the last node of the list
            last=last->next;

        // point last node to next of head or second node of the list
        last->next=(*head)->next;
        free(*head);
        *head=last->next;
    }

    // end of list is reached or node to be deleted not there in the list
    while(last->next!=*head&&last->next->data!=key) {
        last=last->next;
    }
    // node to be deleted is found, so free the memory and display the list
    if(last->next->data==key) {
        d=last->next;
        last->next=d->next;
        cout<<"The node with data "<<key<<" deleted from the list"<<endl;
        free(d);
        cout<<endl;
        cout<<"Circular linked list after deleting "<<key<<" is as follows:"<<endl;
        traverseList(last);
    }
    else
        cout<<"The node with data "<< key << " not found in the list"<<endl;
}

// main Program
int main()
{
    struct Node *last = NULL;

    last = insertInEmpty(last, 30);
    last = insertAtBegin(last, 20);
    last = insertAtBegin(last, 10);
    last = insertAtEnd(last, 40);
    last = insertAtEnd(last, 60);
    last = insertAfter(last, 50,40 );

    cout<<"The circular linked list created is as follows:"<<endl;

    traverseList(last);

    deleteNode(&last,10);

    return 0;
}