Singly-linked list/Reversal: Difference between revisions
no edit summary
No edit summary |
|||
Line 45:
Big fjords vex quick waltz nymph
nymph waltz quick vex fjords Big
</pre>
=={{header|Delphi}}==
{{works with|Delphi|6.0}}
{{libheader|StdCtrls}}
This version uses standard Delphi concepts of block structure, passing objects,
and avoiding pointers where possible. So, for example, here, the problem is broken
down into a set of simple subroutines that take list-objects as arguments. As a
result, they can be used independently on any linked-list. In this way, they could
be used as the basis for a link-list library or linked-list object. Code-reuse is
a fundamental tool for simplifying programing tasks and decreasing errors. So, in
Delphi, even when you are writing simple code, the language encourages you to make
it modular which makes it easy to reuse and easy to incorporate into libraries.
<syntaxhighlight lang="Delphi">
unit ReverseList;
interface
uses StdCtrls;
procedure LinkListTest(Memo: TMemo);
implementation
{}
const TestData: array [0..5] of string = ('Big','fjords','vex','quick','waltz','nymph');
{Structure contains one list item}
type TLinkItem = record
Name: string;
Link: integer;
end;
{Define a dynamic array, linked list type}
type TLinkedList = array of TLinkItem;
{Define actual working linked-list}
var LinkedList: TLinkedList;
procedure AddItem(var LL: TLinkedList; S: string);
{Insert one string in the specified Linked List}
var Inx: integer;
begin
SetLength(LL,Length(LL)+1);
Inx:=High(LL);
LL[Inx].Name:=S;
LL[Inx].Link:=-1;
{if not first entry, link to previous entry}
if Inx>0 then LL[Inx-1].Link:=Inx;
end;
function GetReversedList(LL: TLinkedList): TLinkedList;
{Return the reverse of the input list}
var I,Next: integer;
var SA: array of string;
begin
SetLength(SA,Length(LL));
{Get names in linked order}
Next:=0;
for I:=0 to High(LL) do
begin
SA[I]:=LL[Next].Name;
Next:=LL[Next].Link;
end;
{Insert them in Linked List in reverse order}
for I:=High(SA) downto 0 do AddItem(Result,SA[I]);
end;
function ListToStr(LL: TLinkedList): string;
{Return list as string for printing or display}
var I,Next: integer;
begin
Result:='';
Next:=0;
for I:=0 to High(LL) do
begin
Result:=Result+LL[Next].Name+' ';
Next:=LL[Next].Link;
end;
end;
procedure LinkListTest(Memo: TMemo);
{Routine to test the code}
{returns output string in memo}
var I: integer;
var S: string;
var LL: TLinkedList;
begin
Memo.Clear;
for I:=0 to High(TestData) do AddItem(LinkedList,TestData[I]);
Memo.Lines.Add(ListToStr(LinkedList));
LL:=GetReversedList(LinkedList);
Memo.Lines.Add(ListToStr(LL));
end;
end.
</syntaxhighlight>
{{out}}
<pre>
Big fjords vex quick waltz nymph
nymph waltz quick vex fjords Big
</pre>
| |||