Poj 2965

 

解：状态压缩bfs，只是要优化常数，直接用ac[I, j]表示选择i行j列的状态转移，从我注释的地方能看出我为何tle

//The Pilots Brothers' refrigerator
const
        bili:array[1..4, 1..4]of longint=((1, 1<<1, 1<<2, 1<<3),
                                       (1<<4, 1<<5, 1<<6, 1<<7),
                                       (1<<8, 1<<9, 1<<10, 1<<11),
                                       (1<<12, 1<<13, 1<<14, 1<<15)
                                        );

        wings=(1 << 16 -1)+100;
        inf='1.txt';
type
        data=record
          x, y: longint;
        end;
var
        ac: array[1..4, 1..4]of longint;
        chaos: longint;
        from, q, step: array[0..wings]of longint;
        ans: array[0..wings]of data;
        visit: array[0..wings]of boolean;
procedure init;
var
        i, j, k, tmp: longint;
        c: char;
begin
  fillchar(visit, sizeof(visit), 0);
  from[1] := 0;
  //fillchar(from, sizeof(from), 0);
  //fillchar(step, sizeof(step), 0);

  chaos := 0;
  for i := 1 to 4 do begin
    for j := 1 to 4 do begin
      read(c);
      if c='+' then chaos := chaos or bili[i, j];
    end;
    readln;
  end;
  for i := 1 to 4 do
    for j := 1 to 4 do begin
      tmp := 0;
      for k := 1 to 4 do begin
        tmp := tmp or bili[i, k];
        tmp := tmp or bili[k, j];
      end;
      ac[i, j] := tmp;
    end;
end;

procedure print(xx: longint);
begin
  if from[xx]=0 then exit;
  print(from[xx]);
  with ans[xx] do begin
    writeln(x, ' ', y);
  end;
end;

procedure main;
var
        i, j, k, head, tail, u, tmp: longint;
begin
  head := 0; tail := 1;
  q[tail] := chaos; visit[chaos] := true;
  step[tail] := 0;
  if chaos=0 then begin
    writeln(0);
    exit;
  end;
  repeat
    inc(head);
    u := q[head];
    for i := 1 to 4 do
      for j := 1 to 4 do begin
        tmp := u;
        {for k := 1 to 4 do begin
          tmp := tmp xor ac[i, k];
          tmp := tmp xor ac[k, j];
        end;}
        tmp := tmp xor ac[i, j];
        if not visit[tmp] then begin
          visit[tmp] := true;
          inc(tail);
          q[tail] := tmp;
          with ans[tail] do begin
            x := i; y := j;
          end;
          from[tail] := head;
          step[tail] := step[head] + 1;
          if tmp=0 then begin
            writeln(step[tail]);
            print(tail);
            exit;
          end;
        end;
      end;
  until head = tail;
end;

begin
  assign(input,inf); reset(input);
  init;
  main;
end.