Doubly-linked list/Element removal: Difference between revisions
Content added Content deleted
(Created task referenced in the Linked List page but not present) |
(Added Algol W) |
||
Line 6:
You may wish to use the list element defined in [[Doubly-Linked List (element)]] for the purposes of this task.
=={{header|ALGOL W}}==
Uses the element type and insertion method as in the [[Doubly-Linked List (traversal)]] task.
<lang algolw>begin
% record type to hold an element of a doubly linked list of integers %
record DListIElement ( reference(DListIElement) prev
; integer iValue
; reference(DListIElement) next
);
% additional record types would be required for other element types %
% inserts a new element into the list, before e %
reference(DListIElement) procedure insertIntoDListIBefore( reference(DListIElement) value e
; integer value v
);
begin
reference(DListIElement) newElement;
newElement := DListIElement( null, v, e );
if e not = null then begin
% the element we are inserting before is not null %
reference(DListIElement) ePrev;
ePrev := prev(e);
prev(newElement) := ePrev;
prev(e) := newElement;
if ePrev not = null then next(ePrev) := newElement
end if_e_ne_null ;
newElement
end insertIntoDListiAfter ;
% removes an element e of a doubly linked list %
procedure removeDListIElement( reference(DListIElement) value e );
if e not = null then begin
% have an element to remove %
reference(DListIElement) ePrev, eNext;
ePrev := prev(e);
eNext := next(e);
if ePrev not = null then next(ePrev) := eNext;
if eNext not = null then prev(eNext) := ePrev
end removeDListIElement ;
begin
reference(DListIElement) head, e, toRemove, last;
head := null;
head := insertIntoDListIBefore( head, 1701 );
head := insertIntoDListIBefore( head, 9000 );
e := insertIntoDListIBefore( next(head), 90210 );
toRemove := insertIntoDListIBefore( next(e), 4077 );
e := head;
last := null;
write( "Before: Forward:" );
while e not = null do begin
write( i_w := 1, s_w := 0, " ", iValue(e) );
last := e;
e := next(e)
end while_e_ne_null ;
write( "Before: Backward:" );
e := last;
while e not = null do begin
write( i_w := 1, s_w := 0, " ", iValue(e) );
last := e;
e := prev(e)
end while_e_ne_null ;
e := head;
last := null;
% remove an element %
removeDListIElement( toRemove );
write( "After: Forward:" );
while e not = null do begin
write( i_w := 1, s_w := 0, " ", iValue(e) );
last := e;
e := next(e)
end while_e_ne_null ;
write( "After: Backward:" );
e := last;
while e not = null do begin
write( i_w := 1, s_w := 0, " ", iValue(e) );
last := e;
e := prev(e)
end while_e_ne_null
end
end.</lang>
{{out}}
<pre>
Before: Forward:
9000
90210
4077
1701
Before: Backward:
1701
4077
90210
9000
After: Forward:
9000
90210
1701
After: Backward:
1701
90210
9000
</pre>
|
Revision as of 13:18, 25 September 2020
Doubly-linked list/Element removal is a draft programming task. It is not yet considered ready to be promoted as a complete task, for reasons that should be found in its talk page.
- Task
Define a method to remove an element from a doubly-linked list and demonstrate its use.
You may wish to use the list element defined in Doubly-Linked List (element) for the purposes of this task.
ALGOL W
Uses the element type and insertion method as in the Doubly-Linked List (traversal) task. <lang algolw>begin
% record type to hold an element of a doubly linked list of integers % record DListIElement ( reference(DListIElement) prev ; integer iValue ; reference(DListIElement) next ); % additional record types would be required for other element types % % inserts a new element into the list, before e % reference(DListIElement) procedure insertIntoDListIBefore( reference(DListIElement) value e ; integer value v ); begin reference(DListIElement) newElement; newElement := DListIElement( null, v, e ); if e not = null then begin % the element we are inserting before is not null % reference(DListIElement) ePrev; ePrev := prev(e); prev(newElement) := ePrev; prev(e) := newElement; if ePrev not = null then next(ePrev) := newElement end if_e_ne_null ; newElement end insertIntoDListiAfter ; % removes an element e of a doubly linked list % procedure removeDListIElement( reference(DListIElement) value e ); if e not = null then begin % have an element to remove % reference(DListIElement) ePrev, eNext; ePrev := prev(e); eNext := next(e); if ePrev not = null then next(ePrev) := eNext; if eNext not = null then prev(eNext) := ePrev end removeDListIElement ;
begin reference(DListIElement) head, e, toRemove, last; head := null; head := insertIntoDListIBefore( head, 1701 ); head := insertIntoDListIBefore( head, 9000 ); e := insertIntoDListIBefore( next(head), 90210 ); toRemove := insertIntoDListIBefore( next(e), 4077 ); e := head; last := null; write( "Before: Forward:" ); while e not = null do begin write( i_w := 1, s_w := 0, " ", iValue(e) ); last := e; e := next(e) end while_e_ne_null ; write( "Before: Backward:" ); e := last; while e not = null do begin write( i_w := 1, s_w := 0, " ", iValue(e) ); last := e; e := prev(e) end while_e_ne_null ; e := head; last := null;
% remove an element % removeDListIElement( toRemove );
write( "After: Forward:" ); while e not = null do begin write( i_w := 1, s_w := 0, " ", iValue(e) ); last := e; e := next(e) end while_e_ne_null ; write( "After: Backward:" ); e := last; while e not = null do begin write( i_w := 1, s_w := 0, " ", iValue(e) ); last := e; e := prev(e) end while_e_ne_null end
end.</lang>
- Output:
Before: Forward: 9000 90210 4077 1701 Before: Backward: 1701 4077 90210 9000 After: Forward: 9000 90210 1701 After: Backward: 1701 90210 9000