C 问题 #4 - 双链表从双链表中删除所有奇数

Question

I am trying to delete all odd numbers from a doubly linked list. I understand the rough concept, but I am having trouble with implementing it in C. Hope someone could help me out with this!

This is the code that I wrote for this. All the best!

typedef struct lista
{
    int broj;
    struct lista *prev;
    struct lista *next;
}Lista;

Lista *MakeNew ();
Lista *AllocateNode ();
void AddOnEnd ( Lista **p);
int DeleteOddNumbers( Lista **p );
void PrintList ( Lista *p);

int main()
{
    int i, n; printf("N: "); scanf("%d", &n); putchar('\n');
    Lista *lista_brojeva;
    for ( i = 0; i < n; i++ ) 
        AddOnEnd(&lista_brojeva);
    
    int a; 
    a = DeleteOddNumbers(&lista_brojeva);
    PrintList(lista_brojeva);
}

int DeleteOddNumbers( Lista **p )
{
    Lista *tmp = *p;

    if ( tmp != NULL && tmp->broj % 2 != 0 )
    {
        *p = tmp->next;
        free(tmp);
        return 1;
    }
    else
    {
        while ( tmp != NULL && tmp->broj % 2 != 0 )
            tmp = tmp->next;
        
        if ( tmp == NULL ) return 0;
        
        tmp->prev->next = tmp->next;
        free(tmp);
    }
}

Answer 1

One easy solution would be to allocate a new list and to push each even node back to it, then free the first list. This way, your DeleteOddNumbers function should be very simple:

void delete_odd_numbers(t_lst **lst)
{
    t_lst   *new_lst = NULL;
    t_lst   *tmp = *lst;

    while (tmp)
    {
        if (tmp->value % 2 == 0)
            push_back(&new_lst, tmp->value);
        tmp = tmp->next;
    }
    free_lst(*lst);
    *lst = new_lst;
}