ds-lab-codes/DoublyLL.c

#include <stdio.h>
#include <stdlib.h>
typedef struct element {
    int key;
} element;

typedef struct node *nodeptr;

typedef struct node {
    nodeptr llink;
    element item;
    nodeptr rlink;
} node;

void insert(nodeptr head, int data);
void delete(nodeptr head, nodeptr deleted);
void display(nodeptr head);
nodeptr search(nodeptr head, int key);

int main() {
    int choice, data;
    nodeptr node_to_delete;

    nodeptr head = (nodeptr)malloc(sizeof(node));
    if (head == NULL) {
        fprintf(stderr, "Memory allocation failed for head node.\n");
        exit(1);
    }
    head->llink = head;
    head->rlink = head;

    while (1) {
        printf("\n--- Doubly Linked List Menu ---\n");
        printf("1. Insert (at front)\n");
        printf("2. Delete (by key)\n");
        printf("3. Display List\n");
        printf("4. Exit\n");
        printf("Enter your choice: ");

        scanf("%d", &choice);

        switch (choice) {
            case 1:
                printf("Enter number to insert: ");
                scanf("%d", &data);
                insert(head, data);
                printf("Item %d inserted.\n", data);
                break;

            case 2:
                printf("Enter number to delete: ");
                scanf("%d", &data);

                node_to_delete = search(head, data);

                if (node_to_delete == NULL) {
                    printf("Item %d not found in the list.\n", data);
                } else {

                    delete(head, node_to_delete);
                    printf("Item %d deleted.\n", data);
                }
                break;

            case 3:
                display(head);
                break;

            case 4:
                printf("Exiting program.\n");
                free(head);
                exit(0);

            default:
                printf("Invalid choice. Please try again.\n");
        }
    }

    return 0;
}


void insert(nodeptr head, int data) {
    nodeptr newnode = (nodeptr)malloc(sizeof(node));
    if (newnode == NULL) {
        fprintf(stderr, "Memory allocation failed for new node!\n");
        exit(1);
    }
    newnode->item.key = data;
    newnode->llink = head;
    newnode->rlink = head->rlink;
    head->rlink->llink = newnode;
    head->rlink = newnode;
}


void delete(nodeptr head, nodeptr deleted) {
    if (head == deleted) {
        printf("Deletion of the head node not permitted!\n");
    } else {
        deleted->llink->rlink = deleted->rlink;
        deleted->rlink->llink = deleted->llink;
        free(deleted);
    }
}


nodeptr search(nodeptr head, int key) {
    nodeptr temp = head->rlink;


    while (temp != head) {
        if (temp->item.key == key) {
            return temp;
        }
        temp = temp->rlink;
    }
    return NULL;
}


void display(nodeptr head) {
    nodeptr temp = head->rlink;

    if (temp == head) {
        printf("List is empty.\n");
        return;
    }

    printf("List: ");
    while (temp != head) {
        printf("%d ", temp->item.key);
        temp = temp->rlink;
    }
    printf("\n");
}