Re: can't understand how to move a node of a linked list to another place on the same

[Mehdi Saada <00120260a@gmail.com>]

Le jeudi 18 février 2021 à 08:06:57 UTC+1, gautier...@hotmail.com a écrit :
> > No, I'll run it on paper first, please don't bother yet.
> That's actually the fun part with linked lists.
 
> That's actually the fun part with linked lists. 
I hate that to no end.

I did put up quite the effort so non-ashamedly I beg for help.
Here's it running on paper. Of course it's wrong 'cause the actual result is still A disappearing.

   procedure insertion_X_on_place_Y (Before_X, Before_Y: in t_List) is
      A: constant t_List := Before_X.next;
      Y: constant t_List := Before_Y.next;
   Begin
      Before_X.next := Before_X.next.next;
      X.next := Y;
      Before_Y.next := X;
   end insertion_X_on_place_Y;

Before running:
X		(x)->(x+1)->..
Y		(y)->(y+1)->..
Before_X	(x-1)->(x)->(x+1)...->(Y-1)->(Y)->(y+1)..
Before_X.next	(x)->(x+1)...->(Y-1)->(Y)->(y+1)..
Before_Y	(Y-1)->(Y)->(y+1)..
Before_Y.next	(Y)->(y+1)..

But: I want (x-1)->(x+1)...->(Y-1)->(x)-> (Y)->(y+1)..

Before_X.next := X.next;

X		(x)->(x+1)->..
Y		(y)->(y+1)->..
Before_X	(x-1)-> (x+1)...->(Y-1)->(Y)->(y+1)..
Before_X.next	(x+1)...->(Y-1)->(Y)->(y+1)..
Before_Y	(Y-1)->(Y)->(y+1)..
Before_Y.next	(Y)->(y+1)..

X.next := Y;

X		(x)->(y)->(y+1)->..
Y		(y)->(y+1)->..
Before_X	(x-1)-> (x+1)...->(Y-1)->(Y)->(y+1)..
Before_X.next	(x+1)...->(Y-1)->(Y)->(y+1)..
Before_Y	(Y-1)->(Y)->(y+1)..
Before_Y.next	(Y)->(y+1)..

Before_Y.next := X;

X		(x)->(y)->(y+1)->..
Y		(y)->(y+1)->..
Before_X	(x-1)-> (x+1)...->(Y-1)->(x)->(y)->(y+1)->..
Before_X.next	(x+1)...->(Y-1)->(x)->(y)->(y+1)->..
Before_Y	(Y-1)->(x)->(y)->(y+1)->..
Before_Y.next	(x)->(y)->(y+1)->..
It SHOULD be ok.

then I display it:
insertion_A_on_place_b(List, List.next);
   ITERATOR := List;
   while ITERATOR /= null loop
      Put(ITERATOR.value'Image & ' ');
      ITERATOR := ITERATOR.next;
   end loop;

'1' 
'3' 
'4' 
'5' 

PLEASE HELP.