混合排序小练习

2011 年的最后一天了...

混合排序 -> 搅乱、重新洗牌; 以 Integer 动态数组为例.

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//两个辅助函数 Swap、ToStr, 分别用于交换数组元素和呈现为字符串
procedure Swap(var Arr: TArray<Integer>; a,b: Cardinal);
var
  tmp: Integer;
begin
  if (a >= Length(Arr)) or (b >= Length(Arr)) or (a = b) then Exit;
  tmp := Arr[a];
  Arr[a] := Arr[b];
  Arr[b] := tmp;
end;

function ToStr(const Arr: TArray<Integer>): string;
var
  n: Integer;
begin
  for n in Arr do
    Result := Result + IntToStr(n) + sLineBreak;
end;
//-----------------------------------------------------------------

{1、简单反排序}
procedure SimpleShuffle(var Arr: TArray<Integer>);
var
  r,i: Integer; //分别用作随机索引、遍历索引
begin
  for i := 0 to Length(Arr) - 1 do
  begin
    r := Random(Length(Arr));
    Swap(Arr, i, r);
  end;
end;

{2、好的反排序}
procedure GoodShuffle(var Arr: TArray<Integer>);
var
  r,i: Integer;
begin
  for i := Length(Arr) - 1 downto 0 do
  begin
    r := Random(i + 1);
    if r <> i then Swap(Arr, i, r);
  end;
end;

{测试}
procedure TForm1.Button1Click(Sender: TObject);
var
  arr1,arr2: TArray<Integer>;
begin
  arr1 := TArray<Integer>.Create(0, 1, 2, 3, 4, 5, 6, 7, 8, 9); //
  arr2 := Copy(arr1);                                           //

//  SimpleShuffle(arr2);
  GoodShuffle(arr2);

  Memo1.Text := ToStr(arr1);
  Memo2.Text := ToStr(arr2);
end;

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