#include <stdio.h>
#include <stdlib.h>


typedef struct node {
    int data;
    struct node *prev;
    struct node *next;
} NODE;


NODE *head = NULL;


void insert_front(int value) {
    NODE *newNode = (NODE *)malloc(sizeof(NODE));

    if (newNode == NULL) {
        printf("Memory allocation failed\n");
        return;
    }

    newNode->data = value;
    newNode->prev = NULL;
    newNode->next = head;

    if (head != NULL) {
        head->prev = newNode;
    }

    head = newNode;
    printf("Inserted %d\n", value);
}


void delete_value(int value) {
    NODE *temp = head;

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

    while (temp != NULL) {
        if (temp->data == value) {

            
            if (temp->prev == NULL) {
                head = temp->next;
                if (head != NULL)
                    head->prev = NULL;
            }
        
            else {
                temp->prev->next = temp->next;
                if (temp->next != NULL)
                    temp->next->prev = temp->prev;
            }

            free(temp);
            printf("Deleted %d\n", value);
            return;
        }
        temp = temp->next;
    }

    printf("Value not found\n");
}

void display() {
    NODE *temp = head;

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

    printf("List: ");
    while (temp != NULL) {
        printf("%d <-> ", temp->data);
        temp = temp->next;
    }
    printf("NULL\n");
}


int main() {
    int choice, value;

    while (1) {
        printf("\n--- DOUBLY LINKED LIST MENU ---\n");
        printf("1. Insert at front\n");
        printf("2. Delete by value\n");
        printf("3. Display\n");
        printf("4. Exit\n");
        printf("Enter choice: ");
        scanf("%d", &choice);

        switch (choice) {

            case 1:
                printf("Enter value to insert: ");
                scanf("%d", &value);
                insert_front(value);
                break;

            case 2:
                printf("Enter value to delete: ");
                scanf("%d", &value);
                delete_value(value);
                break;

            case 3:
                display();
                break;

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

            default:
                printf("Invalid choice\n");
        }
    }
}