2 arrays 300 by 1000 give us 600 Kb, not 1000+!
Usually pascal compiler adds 260 kb, but not more than 300!
And when I use only one array a, I get time limit, but with memory
usage of 800K instead of 500! How is this possible? Help me, please!

Program Labyrint;
 Const Max=1000;
 Var a,b:Array[-1..300,-1..Max+1] Of Byte;
     n,m,i,j,x,y,mx,my:Integer;
     m2:Array[0..3] Of Byte;
 Procedure PutV(X,Y:Integer; V:Byte);
  Var dx:Integer;
 Begin
  dx:=m2[X Mod 4];
  X:=X Shr 2;
  a[X,Y]:=a[X,Y] And (255 Xor (3 Shl dx));
  a[X,Y]:=a[X,Y] Or (V Shl dx);
 End;
 Function GetV(X,Y:Integer):Byte;
  Var dx,v:Integer;
 Begin
  dx:=m2[X Mod 4];
  X:=X Shr 2;
  GetV:=(a[X,Y] And (3 Shl dx)) Shr dx;
 End;
 Procedure ReadData;
  Var i,j:Integer;
      s:String;
  Procedure Check(i,j:Integer);
  Begin
   If GetV(i,j)=1 Then
    If GetV(i+1,j)+GetV(i-1,j)+GetV(i,j+1)+GetV(i,j-1)<=1 Then Begin
     x:=i;
     y:=j;
    End;
  End;
 Begin
  Readln(n,m);
  FillChar(a,SizeOf(a),0);
  x:=0; y:=0;
  For i:=1 To m Do Begin
   Readln(s);
   For j:=1 To n Do Begin
    If s[j]='.' Then
     PutV(j,i,1);
    If x=0 Then
     Check(j-1,i-1);
   End;
  End;
  For i:=1 To m Do
   Check(n,i);
  For i:=1 To n Do
   Check(i,m);
 End;
 Procedure FindLone;
  Var i,j:Integer;
 Begin
  x:=0; y:=0;
  For i:=1 To n Do
   For j:=1 To m Do
    If GetV(i,j)=1 Then
     If GetV(i+1,j)+GetV(i-1,j)+GetV(i,j+1)+GetV(i,j-1)<=1 Then Begin
      x:=i;
      y:=j;
      Exit;
     End;
 End;
 Procedure ShowField;
  Var i,j:Integer;
 Begin
  Writeln;
  For i:=1 To m Do Begin
   For j:=1 To n Do
    Write(GetV(j,i));
   Writeln;
  End;
 End;
 Function FindMaxXY(x,y:Integer; Var mx,my:Integer):Integer;
  Var i,j,l,ml,n2:Integer;
  Function Check(dx,dy,v:Integer):Boolean;
  Begin
   If GetV(i+dx,j+dy)=v Then Begin
    i:=i+dx; j:=j+dy;
    If v=1 Then
     Inc(l)
    Else
     Dec(l);
    Check:=True
   End Else
    Check:=False;
  End;
 Begin
  i:=x; j:=y; l:=0; ml:=-1;
  Repeat
   n2:=0;
{   ShowField;
   Readln;}
   If GetV(i,j)=1 Then
    PutV(i,j,2)
   Else Begin
   If GetV(i+1,j)=2 Then Inc(n2);
   If GetV(i-1,j)=2 Then Inc(n2);
   If GetV(i,j+1)=2 Then Inc(n2);
   If GetV(i,j-1)=2 Then Inc(n2);
   If n2<1 Then
   PutV(i,j,GetV(i,j)+1);
   End;
   If Not Check(1,0,1) Then
   If Not Check(-1,0,1) Then
   If Not Check(0,1,1) Then
   If Not Check(0,-1,1) Then Begin
    If l>ml Then Begin
     mx:=i; my:=j;
     ml:=l;
    End;
    If GetV(i,j)=2 Then
     PutV(i,j,3);
    If Not Check(1,0,2) Then
    If Not Check(-1,0,2) Then
    If Not Check(0,1,2) Then
     Check(0,-1,2)
   End;
  Until ((i=x) And (j=y));
 FindMaxXY:=ml;
 End;
Begin
 For i:=0 To 3 Do
  m2[i]:=2*i;
 FillChar(a,SizeOf(a),0);
 ReadData;
 Move(a,b,SizeOf(b));
 If x=0 Then Begin
  Writeln(0);
  Halt;
 End;
 FindMaxXY(x,y,mx,my);
 For i:=1 To n Do
  For j:=1 To m Do
   If GetV(i,j)>0 Then
    PutV(i,j,1);
 Writeln(FindMaxXY(mx,my,x,y));
End.

My algorythm is as follows :
1. Choose any free cell c1 with only 1 or 0 neighbours - O(n*m)
2. Find the cell c2 for wich length of path to c1 is maximum - O(n*m)
3. Find the cell c3 for wich length of path to c2 is maximum - O(n*m)
Then the length of path from c2 to c3 is the answer.
I use width search for steps 2 and 3, so they should run in O(n*m).
And, I only use one array [-1..250,-1..1010] Of Byte! Why does this
program run in 0.98 sec and 885 Kb???
If anyone could help me, email me please and I will send you my code
(I don't leave it here because Marat Bakirov won't be happy to see an
accepted program on the webboard:)

> My algorythm is as follows :
> 1. Choose any free cell c1 with only 1 or 0 neighbours - O(n*m)
> 2. Find the cell c2 for wich length of path to c1 is maximum - O
(n*m)
> 3. Find the cell c3 for wich length of path to c2 is maximum - O
(n*m)
> Then the length of path from c2 to c3 is the answer.
> I use width search for steps 2 and 3, so they should run in O(n*m).
> And, I only use one array [-1..250,-1..1010] Of Byte! Why does this
> program run in 0.98 sec and 885 Kb???
> If anyone could help me, email me please and I will send you my
code
> (I don't leave it here because Marat Bakirov won't be happy to see
an
> accepted program on the webboard:)

> > My algorythm is as follows :
> > 1. Choose any free cell c1 with only 1 or 0 neighbours - O(n*m)
> > 2. Find the cell c2 for wich length of path to c1 is maximum - O
> (n*m)
> > 3. Find the cell c3 for wich length of path to c2 is maximum - O
> (n*m)
> > Then the length of path from c2 to c3 is the answer.
> > I use width search for steps 2 and 3, so they should run in O
(n*m).
> > And, I only use one array [-1..250,-1..1010] Of Byte! Why does
this
> > program run in 0.98 sec and 885 Kb???
> > If anyone could help me, email me please and I will send you my
> code
> > (I don't leave it here because Marat Bakirov won't be happy to
see
> an
> > accepted program on the webboard:)