Question

I’m trying to append two structures into one
Ex.

l1 = add(1, add(2, NULL));
l2 = add(3, add(4, NULL));
myappend(l1,l2) = add(1,add(2,add(3,add(4,NULL))))

I tried many other ways that I can think of… but it doesn’t work… can anyone help me out?

struct list_node {
   struct list_node * rest;
   int first;
};

list add(int in, list l) {
   list r = malloc(sizeof(struct list_node));
   r->first = in;
   r->rest = l;
   return r;
}
// My attempted solution;
list myappend(list l1,list l2){
   list k = malloc(sizeof(struct list_node));
   k=l2;
   k=add(l1,k);
   return k;
}

Answer 1

I guess the type list is struct list_node *. If you can define a type for list, you can define a type for list with a last point to the last node of the list, example:

struct list {
    struct list_node *first;
    struct list_node *last;
}
void myappend(struct list *l1,struct list *l2){
   // check the argument here when needed.

   l1->last->rest = l2->first;
   l1->last = l2->last;
   free(l2);
}

If you want to keep the type list as struct list_node *, you should
1) Ensure the last node(of a list)’s rest is NULL.
2) Loop and find the last node of the fist list and do the merge(just link them).

You can also use recursion code:

list __add(struct list_node *first_node, list rest) { // split your list_add()
   first_node->rest = rest;
   return first_node
}
list add(int in, list l) {
   list r = malloc(sizeof(struct list_node));
   r->rest = NULL;
   r->first = in;
   return __add(r, l);
}
list myappend(list l1,list l2){
   if (l1)
       return __add(l1, myappend(l1->rest, l2));
   else
       return l2;
}