[Usaco2008 Mar]Cow Travelling游荡的奶牛

http://www.lydsy.com/JudgeOnline/problem.php?id=1616

循环写4msAC，记忆化搜索TLE，到底哪里出问题？实在查不出来。

program Travelling;
const dx:array[1..4] of longint=(-1,1,0,0);
      dy:array[1..4] of longint=(0,0,1,-1);
      maxn=100;maxt=15;Filename='Travelling';
var   f:array[0..maxn+1,0..maxn+1,0..maxt] of longint;
      map:array[0..maxn+1,0..maxn+1] of boolean;
      i,j,n,m,t,r1,r2,c1,c2,tmp,k,l,nx,ny:longint;
      ch:char;
procedure DFS(x,y,t:longint);
          var nx,ny,tmp,i:longint;
          begin tmp:=0;
          if(F[x][y][t]<>0)or(t<=0)then exit;
          for i:=1 to 4 do begin
            nx:=x+dx[i];ny:=y+dy[i];
            if map[nx][ny]
              then begin
                   DFS(nx,ny,t-1);
                   inc(tmp,F[nx][ny][t-1]);
                   end;end;
          F[x][y][t]:=tmp;
          end;
begin
fillchar(map,sizeof(map),false);
readln(N,M,T);
for i:=1 to N do begin
  for j:=1 to M do begin
    read(ch);
    if ch='.' then
      map[i][j]:=true;
    end;readln;end;
readln(R1,C1,R2,C2);
F[R1][C1][0]:=1;
for k:=1 to T do
  for i:=1 to n do
    for j:=1 to m do begin
      if not map[i][j]
        then continue;
      tmp:=0;
      for l:=1 to 4 do
        begin
        nx:=i+dx[l];ny:=j+dy[l];
        if map[nx][ny] then
          tmp:=tmp+F[nx][ny][k-1];
        end;
      f[i][j][k]:=tmp;
      end;
writeln(F[R2][C2][T]);
end.