Doubly-linked list/Element removal: Difference between revisions
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</pre>
=={{header|Pascal}}==
==={{header|Free Pascal}}===
<syntaxhighlight lang="pascal">
program doublylinkedlist;
type
pDbllist = ^tDbllist;
tDbllist = record
data: integer;
prev, next: pDbllist;
end;
procedure add(var tail: pDbllist; data: integer);
var
cur: pDbllist;
begin
new(cur);
cur^.data := data;
cur^.prev := tail;
cur^.next := nil;
if tail <> nil then
tail^.next := cur;
tail := cur;
end;
procedure delete(var head, tail: pDbllist; data: integer);
var
cur: pDbllist;
begin
cur := head;
while (cur <> nil) and (cur^.data <> data) do
cur := cur^.next;
if cur = nil then
exit; // data not found
if cur^.prev = nil then // cur is the head
begin
head := cur^.next;
if head <> nil then
head^.prev := nil
else
tail := nil; // list becomes empty
end
else if cur^.next = nil then // cur is the tail
begin
tail := cur^.prev;
tail^.next := nil;
end
else // cur is in the middle
begin
cur^.prev^.next := cur^.next;
cur^.next^.prev := cur^.prev;
end;
dispose(cur);
end;
procedure destroyList(var head: pDbllist);
var
cur, next: pDbllist;
begin
cur := head;
while cur <> nil do
begin
next := cur^.next;
dispose(cur);
cur := next;
end;
head := nil;
end;
procedure display(head: pDbllist);
var
cur: pDbllist;
begin
cur := head;
while cur <> nil do
begin
writeln(cur^.data);
cur := cur^.next;
end;
end;
var
head, tail: pDbllist;
i: integer;
begin
head := nil;
tail := nil;
// Initial list setup
for i := 1 to 5 do
begin
if tail = nil then
begin
new(head);
head^.data := i;
head^.prev := nil;
head^.next := nil;
tail := head;
end
else
begin
add(tail, i);
end;
end;
writeln('Original list:');
display(head);
writeln('Deleting 3:');
delete(head, tail, 3);
display(head);
writeln('Deleting 1 (head):');
delete(head, tail, 1);
display(head);
writeln('Deleting 5 (tail):');
delete(head, tail, 5);
display(head);
writeln('Destroying list!');
destroyList(head);
display(head); // should display nothing as the list is destroyed
end.
</syntaxhighlight>
{{out}}
<pre>
Original list:
1
2
3
4
5
Deleting 3:
1
2
4
5
Deleting 1 (head):
2
4
5
Deleting 5 (tail):
2
4
Destroying list!
</pre>
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