In which case will the command be executed?

[evinda]

Hello! (Wave)

I am looking at an algorithm, that inserts an element in a sorted list:

void llinsert(Type x, pointer L)
       pointer C, ptr; 
       q = L;
       pq = NULL;
       while (q != NULL) and (q->data < x) {
                pq = q;
                q = q->next;
       }
       if (q != NULL) and (q->data == x) then return;

       p = NewCell(Node); 
       p->data = x;
       p->next = q;
       if (pq == NULL) then L = p;
       else pq->next = p;

In which case will the command [m] if (pq == NULL) then L = p; [/m] be executed?

 

[I like Serena]

Hello! (Wave)

I am looking at an algorithm, that inserts an element in a sorted list:

void llinsert(Type x, pointer L)
       pointer C, ptr; 
       q = L;
       pq = NULL;
       while (q != NULL) and (q->data < x) {
                pq = q;
                q = q->next;
       }
       if (q != NULL) and (q->data == x) then return;

       p = NewCell(Node); 
       p->data = x;
       p->next = q;
       if (pq == NULL) then L = p;
       else pq->next = p;

In which case will the command [m] if (pq == NULL) then L = p; [/m] be executed?

Hi! (Happy)

Apparently only if L was NULL to begin with. (Mmm)

 

[johng1]

I think I like Serena meant to say:
If x is smaller that the data of the first node of the list, then the pointer to the first node of the list (namely L) is changed to point to the new first node *p.

 

[evinda]

Hi! (Happy)

Apparently only if L was NULL to begin with. (Mmm)

A ok... I see... (Nod)

 

[I like Serena]

What johng said. (Blush)

 

[evinda]

What johng said. (Blush)

Oh yes, right... But also if L was NULL at the beginning, right?

 

[I like Serena]

Oh yes, right... But also if L was NULL at the beginning, right?

Yep. (Wink)

Variable pq is initially set to NULL, and it only changes if the condition [m](q != NULL) and (q->data < x)[/m] is true at least once.
If that never happens, then that means that either q was NULL at the beginning (meaning L is NULL), or we initially had that [m]q->data >= x[/m], meaning [m]L->data >= x[/m]. (Nerd)

 

[evinda]

I think I like Serena meant to say:
If x is smaller that the data of the first node of the list, then the pointer to the first node of the list (namely L) is changed to point to the new first node *p.

Yep. (Wink)

Variable pq is initially set to NULL, and it only changes if the condition [m](q != NULL) and (q->data < x)[/m] is true at least once.
If the never happens, then that means that either q was NULL at the beginning (meaning L is NULL), or we initially had that [m]q->data >= x[/m], meaning [m]L->data >= x[/m]. (Nerd)

I see.. Thanks a lot! (Smile)