Problem mit Sudoku-Generator

[athomas]

Hallo, ich hab mal versucht einen Sudoku-Generator zu schreiben.
Leider hängt der sich jedesmal auf.
Könnt ihr da mal nen Blick draufwerfen?

Code:

constructor s.create();
var
  i, j: integer;
begin
  for i:=0 to 8 do
    for j:=0 to 8 do
      f[i,j]:=0;
end;

procedure s.generate();
var
  i, j: integer;
  s: string;
begin
  i:=0;
  while i<=8 do
    begin
      j:=0;
      while j<=8 do
        begin
          f[i,j]:=Random(9)+1;
          j:=j+1;
        end;
      if (fArrOK(f))or(i>5) then
        i:=i+1;
    end;
  for i:=0 to 8 do
    begin
      s:=s+#13#10;
    for j:=0 to 8 do
      s:=s+' '+inttostr(f[j,i]);

    end;
  ShowMessage(s);
end;

function s.rArrOK(reihe: rArr): boolean;
var
  i, a: integer;
  b: boolean;
  n: array[1..9] of integer;
begin
  b:=true;
  for a:=1 to 9 do
    n[a]:=0;
  for i:=0 to 8 do
    for a:=1 to 9 do
      if reihe[i]=a then
        n[a]:=n[a]+1;

  for a:=1 to 9 do
    if n[a]>1 then
      b:=false;
  result:=b;
end;

function s.qArrOK(quadrat: qArr): boolean;
var
  i, j, a: integer;
  b: boolean;
  n: array[1..9] of integer;
begin
  b:=true;
  for a:=1 to 9 do
    n[a]:=0;
  for i:=0 to 2 do
    for j:=0 to 2 do
      for a:=1 to 9 do
        if quadrat[i,j]=a then
          n[a]:=n[a]+1;

  for a:=1 to 9 do
    if n[a]>1 then
      b:=false;
  result:=b;
end;

function s.fArrOK(feld: fArr): boolean;
var
  i, j, x, y: integer;
  s, r: rArr;
  q: qArr;
  b: boolean;
begin
  b:=true;
  //Spalten
  for i:=0 to 8 do
    begin
      for j:=0 to 8 do
        s[j]:=f[i,j];
      if not(rArrOK(s)) then
        b:=false;
    end;
  //Reihen
  for i:=0 to 8 do
    begin
      for j:=0 to 8 do
        r[j]:=f[j,i];
      if not(rArrOK(r)) then
        b:=false;
    end;
  //Quadrate
  for i:=0 to 2 do
    for j:=0 to 2 do
      begin
        for x:=0 to 2 do
          for y:=0 to 2 do
            q[x,y]:=f[i*3+x,j*3+y];
        if not(qArrOK(q)) then
          b:=false;
      end;
  result:=b;
end;