Schell Sort
While there are several built in alternatives for sorting, this example is
the shell sort algorithm for the vArray global variable. The
ShellSort procedure needs to know the number of elements in the array to sort,
and whether to sort ascending or descending. The Boolean flag is set to
True for ascending order, and False for descending order. Fill the vArray
elements from index 1 through index Count.
procedure ShellSort(count: integer; b: boolean);
var
i,j,k: integer;
v: variant;
label break;
begin
k:=count div 2;
while k>0 do begin
for i:=k to pred(count) do begin
for j:=i-k+1 downto 1 do begin
if b then begin
if vArray(j)<=vArray(j+k)
then goto break;
end
else
if vArray(j)>=vArray(j+k)
then goto break;
v:=vArray(j); {exchange
j and j+k elements}
SetArray(j,vArray(j+k));
SetArray(j+k,v);
end;
break: end;
k:=k div 2;
end;
end;
var n: integer;
begin
if who=1 then begin
Output(eClear);
DimArray(20); {when you use vArray
don't forget to dimension it}
for n:=1 to 20 do SetArray(n,Random(100));
ShellSort(20,true);
for n:=1 to 20 do writeln(vArray(n));
end;
end;
Notes: You may want to file this example away in your collection
of useful routines. Note, the TArray variables have a built in
sort method which would be used for TArray variables instead of a
routine like today's example.
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