gistfile1.c

#include <cs50.h>
#include <stdio.h>

typedef struct dllist {
    int n;
    struct dllist* prev;
    struct dllist* next;
}
dllnode;

dllnode* create_dll(int n) {
    dllnode* new = malloc(sizeof(dllnode));
    if (new == NULL)
        exit(1);
    new->n = n;
    new->prev = NULL;
    new->next = NULL;
    return new;
}

dllnode* insert_dll(dllnode* first, int n) {
    dllnode* new = malloc(sizeof(dllnode));
    if (new == NULL)
        exit(1);
    new->n  = n;
    new->next = first;
    new->prev = NULL;
    first->prev = new;
    first = new;
    return new;
}


dllnode* target_to_del(dllnode* first, int n) {
    dllnode* trav = first;
    while (trav != NULL) {
        if (trav->n == n)
            return trav;
        trav = trav->next;
    }
    return 0;
}


void delete_dllnode(dllnode* target) {
    if (target->prev != NULL && target->next != NULL) {
        dllnode* prev = target->prev;
        dllnode* next = target->next;
        prev->next = next;
        next->prev = prev;
    }
    else if (target->prev == NULL && target->next != NULL) {
        dllnode* next = target->next;
        next->prev = NULL;
    }
    else if (target->prev != NULL && target->next == NULL) {
        dllnode* prev = target->prev;
        prev->next = NULL;
    }
    free(target);
}

int main(void) {
    dllnode* new = create_dll(6);
    for (int i = 0; i < 6; i++)
        new = insert_dll(new, i);
    int n = get_int();
    dllnode* target = target_to_del(new, n);
    delete_dllnode(target);
    dllnode* trav = new;
    while (trav != NULL) {
        printf("%i ", trav->n);
        trav = trav->next;
    }
    printf("\n");
}