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;
}