# efficient way of collating (mixing) two linked lists using C

Discussion in 'Embedded' started by s_subbarayan, Mar 3, 2005.

1. ### s_subbarayanGuest

Dear all,
1)In one of our implementation for an application we are supposed to
collate two linked lists.The actual problem is like this:

There are two singularly linked lists, the final output will be a
"perfectly shuffle" of the lists together into a single list. The new
list should consist of consecutively alternating nodes from both
lists.Note that both these linked lists have same kind of data
structure in their nodes.

solution:
The logic which I thought for implementing this is to create temporary
node which resembles the nodes in the input linked lists and then copy
second node into it,swap the pointers to insert the second lists first
node into the first lists second node and proceed so on recursively by
inserting the second lists node in between the first lists node.

Is my thinking correct?I believe this is not that efficient way of
doing it.Can some one let me know how effectively should we implement
this collation between two linked lists?

2)I came across the following code snippet regarding linked lists:
struct _tagElement
{
int m_cRef;
unsigned char m_bData[20];
struct _tagElement * m_next;

} NODE, * PNODE;

PNODE DoesWhat (PNODE pn1, PNODE pn2)
{
PNODE * ppnV = &pn1;
PNODE * ppn1 = &pn1;
PNODE * ppn2 = &pn2;

for ( ; *ppn1 || *ppn2; ppn1 =
&((*ppn1)->m_next))
{
if (!(*ppn1) || (0 <
memcmp((*ppn1)->m_bData, (*ppn2)->m_bData,
sizeof((*ppn2)->m_bData))))
{
PNODE pn = *ppn1;
*ppn1 = *ppn2;
pn2 = (*ppn2)->m_next;
(*ppn1)->m_next = pn;
}
}
return *ppnV;
}
I inferred from this code,that the actual functionality of the function
"DoesWhat" is to collate two linked list as stated in query (1)
referred in this post.But my friend disagrees.I said that the function
doeswhat takes first node of two linked lists(pn1 is first node of
not be correct!)),and the code inside inserts nodes of list2 into nodes
of list1,also the list will be sorted in increasing order of number of
characters present in the array m_bData.
Is my understanding and assumption regarding the input params for
function "doeswhat" correct?Note that I dont have full code with me,so
this code puzzled me,so I have to make it out myself!.

Sorry if it looks too immature to ask,but I thought better learn now
then never.I wish I am able to prove to my friend that I am
correct,though I am ready to accept my fault incase I am disproved with
proper proof.

I appologise incase this OT.Please refer me to proper group incase this
is OT.

Regards,
s.subbarayan

s_subbarayan, Mar 3, 2005

2. ### CBFalconerGuest

Answer deleted due to later discovery that the OP multi-posted the
same query on at least one other newsgroup. This obnoxious
behaviour should not be rewarded.

CBFalconer, Mar 3, 2005

3. ### DaveGuest

The self appointed usenet police.

Yes I top posted to annoy you.

Dave, Mar 3, 2005
4. ### CBFalconerGuest

Good b....LONK.

CBFalconer, Mar 3, 2005
5. ### JoeGuest

Did you have a bad day (or something?) and just do the usenet equivalent of
'going postal' on the OP?

Joe, Mar 3, 2005
6. ### Rufus V. SmithGuest

The insistence on posting to one-and-only-one newsgroup is
a bit anal. Unless the objection is to the multi-post, rather
than appropriately cross-posting. But never attribute to
obnoxiousness what can be reasonable explained by ignorance.

The status can be upgraded to obnoxious upon discovery this
is not the OP's first offense...

Rufus

Rufus V. Smith, Mar 3, 2005
7. ### Richard HenryGuest

Richard Henry, Mar 3, 2005
8. ### CBFalconerGuest

Having the same message come up and waste my (and others) time and
storage in multiple newsgroups. This is what cross-posting is for,
to attract attention from a variety of areas, PROVIDED that
follow-ups are immediately set to concentrate the answers in a

I found the multi-post on at least three newsgroups that I
monitor. That means he probably did it to many more. I see no
reason why usenet posters should not read and absorb some of the
literature available on netiquette and usage.

I will confess to feeling somewhat peckish when I posted that
reply. But why should I go out of my way to help someone who comes
across as too careless to observe the proprieties? At least I did
him the courtesy of telling him WHY I am ignoring him.

CBFalconer, Mar 3, 2005
9. ### Jan HomuthGuest

The correct group is: comp.lang.c or comp.lang.c.moderated, I guess

Your question sounds very much like a homework and it would be smart if
you would lead the discussion with your friend (his name 'professor ? )
to its end.
Thereby learning...

A very good reference for general wisdom on C :
"The C Programming Language" by Kernighan & Ritchie

Also consider to get Robert Sedgewick's "Algorithms in C"

grtnx
/jan

Jan Homuth, Mar 3, 2005
10. ### s_subbarayanGuest

Mr.CBF,
I have informed and even appologised if this post is OT.Further
while I appreciate your comments in making this usenet clean I believe
you can be polite and polished being an experienced professional.Simply
bashing a poster will only discourage some one from using the usenet in
a proper manner.While I agree that following few etiquettes is
important,forget me,no one would like to get bashing from some
unauthorised usenet controller.I believe only the moderator has right
to say whats correct or whats wrong with a particular post!

I posted this query in multiple groups jus to attract different
opinion.Further In same group some time back I saw some one bashing for
cross posting.In silence of moderator ubiquitous gurus sprang up and
bash something making the discussion unhealthy!Had I cross posted I
believe it could become more of a sort of debate on whose algorithm is
best and viceversa which is not in my concern of the query.I feel if
you are not interested you need not post your reply.There are many
people who may be interested to reply.Further seeing the topic or query
in the subject line one can easily judge whether the topic appeared in
different group or not.Then I believe if you saw same post in some
other group,you need not waste your time in reading it again and then
waste your time and resources in bashing some poster like me.While you
regarding time.There are many people out there who are not visiting
multiple groups,so I can get various replys from those people.
On a softer note,please avoid bossy attitude.Everyone is a learner and
there are lot to know.Known is a drop,unknown is a ocean!The query I
posted is not meant to waste someones time!Its meant for a healthier
discussion.But rather you moved away from crux of the problem!

Regards,
s.subbarayan

s_subbarayan, Mar 4, 2005
11. ### prashanth b sGuest

Hello Subba,
enappa idu ena ayichi??

prashanth b s, Mar 4, 2005
12. ### CBFalconerGuest

This is an unmoderated group, as are the others on which I found
your posts. Only you know where you actually posted, so only you
can set up a proper cross-posting with follow-ups set.

I am not feeling quite as mean today as I was then. The objective,
as ever, is to educate the newbies on usenet so that they don't do
these foolish things. I notice you still did not quote any
material to which you are replying, and have ignored the advice in
my sig. below. This does not bode well for your ability to learn.

CBFalconer, Mar 4, 2005
13. ### s.subbarayanGuest

Mr.CBF,
Its good to know you are interested in educating the newby users of
usenet.But I believe there are better ways of educating from the
approach what you have taken.Looks like bashing to me or any one who
reads this.I feel better way is to put anything you want to say in
softer note then using harsh words like "foolishness" again in your
reply.I believe more then being a professional its good if we are
first of all good human beings.While you take interest in educating
others,it will be better if you put things in proper way so people get
it in right manner.You said I have not learnt to put reply,but it
seems you too should be able to learn using polite soft words.By the
way the problem why my reply message appeared to you like that(not
following quote!) partly because of the problem with google.I still
get the old version of usenet in my webpage which did not show any
options what you have put in your quote!If only its updated I would be
happy enough to follow good things if put in proper way!

Regards,
s.subbarayan

s.subbarayan, Mar 7, 2005