计算123456789，所有3位数加法的组合。

three_num_add.dpr

program three_num_add;

{$APPTYPE CONSOLE}

uses
  Classes,
  SysUtils;

type
  PResult = ^TResult;
  TResult = record
    x, y, z: Integer;
  end;

var
  result_list: TList;

procedure gen_result();
var
  simple_list: TList;

  procedure gen_all_number();
  var
    a, b, c, num: Integer;
  begin
    for a := 1 to 9 do
      for b := 1 to 9 do
        for c := 1 to 9 do
          if (a <> b) and (a <> c) and (b <> c) then
          begin
            num := a * 100 + b * 10 + c;
            simple_list.Add(Pointer(num));
          end;
  end;

  procedure calc_result(x, y, z: Integer);
  type
    TNumbers = set of 1 .. 9;
  var
    x_set, y_set, z_set: TNumbers;
    res: PResult;
  begin
    if (z >= 987) or (simple_list.IndexOf(Pointer(z)) < 0) then
      Exit;

    x_set := [x div 100, (x mod 100) div 10, x mod 10];
    y_set := [y div 100, (y mod 100) div 10, y mod 10];
    z_set := [z div 100, (z mod 100) div 10, z mod 10];
    if (x_set * y_set = []) and (x_set * z_set = []) and (z_set * y_set = []) then
    begin
      GetMem(res, SizeOf(TResult));
      res^.x := x;
      res^.y := y;
      res^.z := z;
      result_list.Add(res);
    end;
  end;

var
  x, y: Integer;
  I, J: Integer;
  test_list: TList;
begin
  simple_list := TList.Create;
  gen_all_number();
  test_list := TList.Create;
  for I := 0 to simple_list.Count - 1 do
  begin
    test_list.Assign(simple_list);
    test_list.Delete(I);
    x := Integer(simple_list[I]);
    for J := 0 to test_list.Count - 1 do
    begin
      y := Integer(test_list[J]);
      calc_result(x, y, x + y);
    end;
  end;
  test_list.Free;
  simple_list.Free;
end;

procedure filter_result();
var
  I, J: Integer;
  temp_list1, temp_list2: TList;
  x1, y1, x2, y2: Integer;
begin
  temp_list1 := TList.Create;
  temp_list1.Assign(result_list);
  temp_list2 := TList.Create;
  temp_list2.Assign(result_list);

  for I := 0 to temp_list1.Count - 1 do
  begin
    for J := 0 to temp_list2.Count - 1 do
    begin
      if I = J then
        Continue;

      x1 := PResult(temp_list1[I])^.x;
      y1 := PResult(temp_list1[I])^.y;
      x2 := PResult(temp_list2[J])^.x;
      y2 := PResult(temp_list2[J])^.y;
      if (x1 = y2) and (x2 = y1) then
      begin
        PResult(result_list[J])^.x := 0;
      end;
    end;
  end;
  temp_list1.Free;
  temp_list2.Free;
end;

procedure print_result();
var
  I: Integer;
  res: PResult;
begin

  for I := 0 to result_list.Count - 1 do
  begin
    res := result_list[I];
    if res^.x <> 0 then
      Writeln(IntToStr(res^.x) + '+' + IntToStr(res^.y) + '=' + IntToStr(res^.z));
  end;
end;

var
  I: Integer;
begin

  result_list := TList.Create;
  gen_result();
  filter_result();
  print_result();

  for I := 0 to result_list.Count - 1 do
    FreeMem(result_list[I]);
  result_list.Free;
end.

牛逼！！！