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在 http://stackoverflow.com/questions/22342854/what-is-the-optimal-algorithm-for-the-game-2048/22389702#22389702 上有很多大牛提出了自己的解决方法。

ovolve 使用了 a-b剪枝，这是典型的用在博弈上的算法，比如：之前的中国象棋就是用了这个方法。

Nicola Pezzotti 的特点在于贡献了一个很简易的计算局面整洁度的算法…..

问题是上面的都是 js 语言编写的，对于我来说很难理解，并且很难进行评估。

个人感觉算法本身不难，困难的是如何理解他们使用的数据结构，更具体来说困难度在于如何进行局面评估的算法（这个问题中，需要对盘面顺序程度和整体分数进行评估）。

最终，目光落在 nneonneo 的算法上。他使用了 bit-map 的技术，能够充分利用空间：每一个格子从 0-15 ，对应着 2^0 – 2^15 ，整个局面用64位即可表示。这样做大大

降低了传递参数之类的耗时，客观上节省了时间。此外，还使用数组直接存放了行列的分数，评估行列分数直接让数组值相加即可，这是非常经典的空间换时间的做法。

他的程序可以在他的 git上下载到 https://github.com/nneonneo/2048-ai ，我这里也存了一份可以在 vs2008下编译通过的

nneonneo

我的程序完全仿照了他的程序，只是没有实现他用来剪枝的泛型 typedef std::map trans_table_t; 因为我使用的 Delphi 2010 没有对应的功能，

在我的 I5 2450 上，一步大约需要2s左右。

program NeoNeo;

{$APPTYPE CONSOLE}

uses
  SysUtils,math,windows;

const
  ROW_MASK=$FFFF;
  COL_MASK=$000F000F000F000F;
  CPROB_THRESH_BASE = 0.0001;
  CACHE_DEPTH_LIMIT=1;
  SEARCH_DEPTH_LIMIT=3;
  b:array[0..13] of integer=(0,2,4,8,16,32,64,128,256,512,1024,2048,4096,8192);
type
  board_t=int64;
  row_t=word;
  get_move_func_t = function(board:board_t):integer;
  T_eval_state=record
         cprob_thresh:single;
         maxdepth:integer;
         curdepth:integer;
         cachehits:integer;
         moves_evaled:integer;
       end;

  function score_tilechoose_node(var state:T_eval_state; board:board_t; cprob:single):single; forward;
  function reverse_row(row:row_t):row_t;  forward;
  function pack_col(col:board_t):row_t; forward;
  function unpack_col(row:row_t):board_t; forward;
  function score_move_node(Var state:t_eval_state;board:board_t; cprob:single):single; forward;

var
  row_left_table:array[0..65535] of board_t;
  row_right_table:array[0..65535] of board_t;
  col_up_table:array[0..65535] of board_t;
  col_down_table:array[0..65535] of board_t;
  line_heur_score_table:array[0..65535] of single;
  row_score_table:array[0..65535] of single;

procedure init_move_tables;
var
  row:LongWord;
  line:array[0..3] of LongWord;
  result:row_t;
  i,j:integer;
begin
  fillchar(row_left_table,0,sizeof(row_left_table));
  fillchar(row_right_table,0,sizeof(row_right_table));
  fillchar(col_up_table,0,sizeof(col_up_table));
  fillchar(col_down_table,0,sizeof(col_down_table));

  for  row:= 0 to 65535 do
    begin
      line[0]:=row and $f;
      line[1]:=(row shr 4) and $f;
      line[2]:=(row shr 8) and $f;
      line[3]:=(row shr 12) and $f;

      i:=0;
      while (i<3) do
        begin
          j:=i+1;
          //for j := i+1 to 3 do
          while (j<4) do
            begin
              if line[j]<>0 then
                  break;
              inc(j);
            end;
          if (j=4) then break;
          if (line[i]=0) then
             begin
               line[i]:=line[j];
               line[j]:=0;
               dec(i);
             end
          else
            if (line[i]=line[j]) and (line[i]<>$f) then
               begin
                 inc(line[i]);
                 line[j]:=0;
               end;
          inc(i);
        end;

      result:=(line[0]) or (line[1] shl 4) or (line[2] shl 8) or (line[3] shl 12);

      row_left_table[row]:=row xor result;
      row_right_table[reverse_row(row)]:=reverse_row(row) xor reverse_row(result);
      col_up_table[row] := unpack_col(row) xor unpack_col(result);
      col_down_table[reverse_row(row)]:=unpack_col(reverse_row(row)) xor unpack_col(reverse_row(result));
    end;
end;

function execute_move_0(var board:board_t):board_t;
var
  tmp:board_t;
  ret:board_t;
begin
  ret:=board;

  tmp:=col_up_table[pack_col((board shr (4*0))and $000F000F000F000F)];
  ret:=ret xor (tmp shl (4*0));

  tmp:=col_up_table[pack_col((board shr (4*1))and $000F000F000F000F)];
  ret:=ret xor (tmp shl (4*1));

  tmp:=col_up_table[pack_col((board shr (4*2))and $000F000F000F000F)];
  ret:=ret xor (tmp shl (4*2));

  tmp:=col_up_table[pack_col((board shr (4*3))and $000F000F000F000F)];
  ret:=ret xor (tmp shl (4*3));

  Result:=ret;
end;

function execute_move_1(var board:board_t):board_t;
var
  tmp:board_t;
  ret:board_t;
begin
  ret:=board;

  tmp:=col_down_table[pack_col((board shr (4*0))and $000F000F000F000F)];
  ret:=ret xor (tmp shl (4*0));

  tmp:=col_down_table[pack_col((board shr (4*1))and $000F000F000F000F)];
  ret:=ret xor (tmp shl (4*1));

  tmp:=col_down_table[pack_col((board shr (4*2))and $000F000F000F000F)];
  ret:=ret xor (tmp shl (4*2));

  tmp:=col_down_table[pack_col((board shr (4*3))and $000F000F000F000F)];
  ret:=ret xor (tmp shl (4*3));

  Result:=ret;
end;

function execute_move_2(var board:board_t):board_t;
var
  tmp:board_t;
  ret:board_t;
begin
  ret:=board;

  tmp:=row_left_table[board shr (16*0) and $FFFF];
  ret:=ret xor (tmp shl (16*0));

  tmp:=row_left_table[board shr (16*1) and $FFFF];
  ret:=ret xor (tmp shl (16*1));

  tmp:=row_left_table[board shr (16*2) and $FFFF];
  ret:=ret xor (tmp shl (16*2));

  tmp:=row_left_table[board shr (16*3) and $FFFF];
  ret:=ret xor (tmp shl (16*3));

  Result:=ret;
end;

function execute_move_3(var board:board_t):board_t;
var
  tmp:board_t;
  ret:board_t;
begin
  ret:=board;

  tmp:=row_right_table[board shr (16*0) and $FFFF];
  ret:=ret xor (tmp shl (16*0));

  tmp:=row_right_table[board shr (16*1) and $FFFF];
  ret:=ret xor (tmp shl (16*1));

  tmp:=row_right_table[board shr (16*2) and $FFFF];
  ret:=ret xor (tmp shl (16*2));

  tmp:=row_right_table[board shr (16*3) and $FFFF];
  ret:=ret xor (tmp shl (16*3));

  Result:=ret;
end;

function pack_col(col:board_t):row_t;
begin
  Result:=col or (col shr 12) or (col shr 24) or (col shr 36);
end;

function unpack_col(row:row_t):board_t;
var
  tmp:board_t;
begin
  tmp:=row;
  Result:=(tmp or (tmp shl 12) or (tmp shl 24) or (tmp shl 36)) and COL_MASK;
end;

procedure print_board(board:board_t);
var
  i:integer;
begin
  for i := 0 to 3 do
    begin
      writeln(format('%4d %4d %4d %4d',
               [b[board and $f],
                b[board shr 4 and $f],
                b[board shr 8 and $f],
                b[board shr 12 and $f]]));
      board:=board shr 16;
    end;
end;

function reverse_row(row:row_t):row_t;
begin
  Result:=((row shr 12) or ((row shr 4) and $F0) or ((row shl 4) and $0F00) or (row shl 12));
end;

function execute_move(move:integer;board:board_t):Board_t;
begin
  case move of
     0://up
       begin
         Result:=execute_move_0(board);
       end;
     1://down
       begin
         Result:=execute_move_1(Board);
       end;
     2://left
       begin
         Result:=execute_move_2(board);
       end;
     3://right
       begin
         Result:=execute_move_3(Board);
       end;
     else
       Result:=0;
  end;
end;

function get_max_rank(board:board_t):integer;
var
  maxrank,k:integer;
begin
  maxrank:=0;
  while board<>0 do
    begin
      k:=board and $f;
      if k>maxrank then maxrank:=k;
      board:=board shr 4;
    end;
  Result:=maxrank;
end;

procedure init_score_tables;
var
  row:Longword;
  i,maxi:integer;
  heur_score:single;
  score:single;
  line:array[0..3] of LongWord;
  rank,maxrank:LongWord;
begin
  fillchar(line_heur_score_table,0,sizeof(line_heur_score_table));
  fillchar(row_score_table,0,sizeof(row_score_table));

  for row:= 0 to 65535 do
    begin

  line[0]:=row and $f;
  line[1]:=(row shr 4) and $f;
  line[2]:=(row shr 8) and $f;
  line[3]:=(row shr 12) and $f;

      heur_score:=0;
      score:=0;

      for i := 0 to 3 do
        begin
          rank:=line[i];

          if (rank=0) then
            begin
              heur_score:=heur_score+10000;
            end
          else
            if (rank>=2) then
              begin
                score:=score+(rank-1)*power(2,rank);
              end;
        end;

      maxi:=0;
      maxrank:=0;
      for i := 0 to 3 do
        begin
          rank:=line[i];
          if (rank>maxrank) then
             begin
               maxrank:=rank;
               maxi:=i;
             end;
        end;

      if (maxi=0) or (maxi=3) then
        heur_score:=heur_score+20000;

      for i := 1 to 3 do
        if (line[i]=line[i-1]+1) or (line[i]=line[i-1]-1) then
             heur_score:=heur_score+1000;

      if (line[0]<line[1]) and (line[1]<line[2]) and (line[2]<line[3]) then
         heur_score:=heur_score+10000;
      if (line[0]>line[1]) and (line[1]>line[2]) and (line[2]>line[3]) then
         heur_score:=heur_score+10000;

      row_score_table[row]:=score;
      line_heur_score_table[row]:=heur_score;
    end;
end;

{
function score_board(board:board_t;tbl):single;
begin
  Result:=(tbl[board and row_mask])+
          (tbl[board shr 16 and row_mask])+
          (tbl[board shr 32 and row_mask])+
          (tbl[board shr 48 and row_mask]);
end;

function score_col_board(board:board_t;tbl):single;
begin
  Result:=(tbl[pack_col[board and col_mask]])+
          (tbl[pack_col[board shr 4 and col_mask])+
          (tbl[pack_col[board shr 8 and col_mask])+
          (tbl[pack_col[board shr 12 and col_mask]);
end;
}
function score_heur_board(board:board_t):single;
begin
  Result:=(line_heur_score_table[board and row_mask])+
          (line_heur_score_table[board shr 16 and row_mask])+
          (line_heur_score_table[board shr 32 and row_mask])+
          (line_heur_score_table[board shr 48 and row_mask])+
          (line_heur_score_table[pack_col(board and col_mask)])+
          (line_heur_score_table[pack_col(board shr 4 and col_mask)])+
          (line_heur_score_table[pack_col(board shr 8 and col_mask)])+
          (line_heur_score_table[pack_col(board shr 12 and col_mask)])+100000;
end;

function score_board(board:board_t):single;
begin
  result:=(row_score_table[board and row_mask])+
          (row_score_table[(board shr 16) and row_mask] )+
          (row_score_table[(board shr 32) and row_mask])+
          (row_score_table[(board shr 48) and row_mask]);
end;

function score_tilechoose_node(var state:T_eval_state; board:board_t; cprob:single):single;
var
  res:single;
  num_open,i:integer;
begin
  res:=0;
  num_open:=0;

  for i:=0 to 15 do
    begin
      //tmp:=board shr (4*i);
    if (board shr (4*i) and $f)=0 then
      inc(num_open);
    end;

  cprob:=cprob /num_open;

  for i := 0 to 15 do
    begin
      if ((board shr (4*i)) and $f =0) then
        begin
          res:=res+score_move_node(state,board or (Board_t (1) shl (4*i)),cprob *0.9) *0.9;
          res:=res+score_move_node(state,board or (Board_t (2) shl (4*i)),cprob *0.1) *0.1;
        end;
    end;

  Result:=Res / num_open;
end;

function score_move_node(Var state:t_eval_state;board:board_t; cprob:single):single;
var
  move:integer;
  best:single;
  res:single;
  newboard:board_t;
  //i:IsingleMapIterator;
begin
  if (cprob<state.cprob_thresh) or (state.curdepth >= SEARCH_DEPTH_LIMIT) then
    begin
      if (state.curdepth > state.curdepth) then
        begin
          state.maxdepth:=state.curdepth;
        end;
      Result:=score_heur_board(board);
      exit;
    end;

{   if (state.curdepth < CACHE_DEPTH_LIMIT) then
     begin
//       i:=state.trans_table.Find(board);
       if state.trans_table.Count(board)>0 then
         begin
           inc(state.cachehits,1);
           Result:=state.trans_table.Find(board).Value;
           exit;
         end;

     end;    }
   best:=0;

   inc(state.curdepth);
   for move := 0 to 3 do
     begin
       newboard:=execute_move(move,board);
       inc(state.moves_evaled);
       if (board = newboard) then
         continue;
       res:=score_tilechoose_node(state,newboard,cprob);
       if res > best then
         best:=res;
     end;
   dec(state.curdepth);

   {if state.curdepth < CACHE_DEPTH_LIMIT then
     begin end; //state.trans_table[board]:=best;}

   result:=best;
end;

function t_score_toplevel_move(var state:t_eval_state;board:board_t;move:integer):single;
var
  newboard:board_t;
begin
  newboard:=execute_move(move,board);
  if board=newboard then
    begin
      Result:=0;
      exit;
    end;

  state.cprob_thresh:=CPROB_THRESH_BASE;

  Result:=score_tilechoose_node(state,newboard,1)+1e-6;
end;


function score_toplevel_move(board:board_t; move:integer):single;
var
  res:single;
  start,finish:DWORD;
  state:t_eval_state;
begin

  state.cprob_thresh:=0;
  state.maxdepth:=0;
  state.curdepth:=0;
  state.cachehits:=0;
  state.moves_evaled:=0;

  start:=GetTickCount;
  res:=t_score_toplevel_move(state,board,move);
  finish:=GetTickCount;

  writeln(format('Move %d: result %f: eval %d moves ',
      [move,res,state.moves_evaled])+'in '+IntToStr(Finish-Start)+' ms');
  result:=res;
end;

function find_best_move(board:board_t):integer;
var
   move:integer;
   best:single;
   bestmove:integer;
   res:single;
begin
  best:=0;
  bestmove:=-1;

  print_board(board);
  writeln(format('Current scores: heur %.0f, actual %.0f',[score_heur_board(board),score_board(board)]));
  for move := 0 to 3 do
    begin
      res:=score_toplevel_move(board,move);
      if (res>best) then
        begin
          best:=res;
          bestmove:=move;
        end;
    end;
  Result:=bestmove;
end;

function draw_tile:integer;
begin
  if Random(9)=0 then Result:=2
  else  Result:=1;
end;

function insert_tile_rand(board:board_t;tile:integer):board_t;
var
  num_open:integer;
  i,index:integer;
  tmp:board_t;
begin
  num_open:=0;
  for i := 0 to 15 do
    if (board shr (4*i) and $f)=0 then
      begin
        inc(num_open)
      end;
  if num_open =0 then
    begin
      writeln('insert_tile_rand:no open spots!');
      Result:= board;
      exit;
    end;

  index:=random(num_open);
  for i := 0 to 15 do
    begin
      if ((board shr (4*i))and $f)<>0 then
         continue;
      if (index=0) then
         begin
           tmp:=tile;
           board:=board or (tmp shl (4 *i));
           break;
         end;
      dec(index);
    end;
  Result:=board;
end;

function initial_board:board_t;
var
   board:board_t;
   i:integer;
begin
  randomize;
  board:=0;
  for i := 0 to 1 do
    board:=insert_tile_rand(board,draw_tile);
  Result:=board;
end;

procedure play_game(get_move:get_move_func_t);
var
  board:board_t;
  moveno:integer;
  scorepenalty:integer;
  move:integer;
  newboard:board_t;
  tile:integer;
begin

  board:=initial_board;

  moveno:=0;
  scorepenalty:=0;

  while True do
    begin
      move:=0;
      while move<4 do
        begin
          if execute_move(move,board)<>board then
              break;
          inc(move);
        end;

      if move=4 then break;

      inc(moveno);
      writeln(format('Move %d , current score=%.0f, %d',[moveno,score_board(board)-scorepenalty,scorepenalty]));

      move:=get_move(board);
      if (move < 0) then break;

      newboard:=execute_move(move,board);
      if (newboard=board) then
        begin
          writeln('Illegal move!');
          dec(moveno);
          continue;
        end;

      tile:=draw_tile;
      if tile=2 then inc(scorepenalty,4);
      board:=insert_tile_rand(newboard,tile);
      writeln;
    end;
   print_board(board);
   writeln(Format('Game Over. Your score is %.0f. The hightest rank you achieved was %d.',[score_board(board)-scorepenalty,get_max_rank(board)]));
end;

//Main
begin
  init_move_tables;
  init_score_tables;
  play_game (find_best_move);
  readln;
end.

目前上面这个程序可以达到 1024 （超长发挥可以达到2048）

后面会进行的改进：

1.使用整数代替程序中的single进行局面分数的评估。

2.实现nneonneo的剪枝算法，计划使用HouSisong大牛的DGL泛型库 http://blog.csdn.net/housisong/article/category/152693

2014/4/26 修正了盘面分数的问题：

修改之前
res:=res+score_move_node(state,board or 1 shl (4*i),cprob *0.9) *0.9;

修改之后
res:=res+score_move_node(state,board or (Board_t (1) shl (4*i)),cprob *0.9) *0.9;