（棋盘覆盖问题）在一个2k×2 k个方格组成的棋盘中恰有一个方格与其它方格不同（图中标记为-1的方格），称之为特殊方格。现用L型（占3个小方格）纸片覆盖棋盘上除特殊方格的所有部分，各纸片不得重叠，于是，用到的纸片数恰好是（4 k-1）/3。在下表给出的一个覆盖方案中，k=2，相同的3各数字构成一个纸片。
下面给出的程序使用分治法设计的，将棋盘一分为四，依次处理左上角、右上角、左下角、右下角，递归进行。请将程序补充完整。

Program j402; 
type arr1=array[1..65] of integer; 
arr2=array[1..65] of arr1; 
var board:arr2; tile:integer; size,dr,dc:integer; 
procedure chessboard(tr,tc:integer; dr,dc:integer; var size:integer); 
var t,s:integer; 
begin 
if (size=1) then ___exit______; 
t:=tile; inc(tile); 
s:=size div 2; 
if then chessboard(tr,tc,dr,dc,s) else begin 
board[tr+s-1]:=t; 
_____(dr<tr+s)and(dc<tc+s)______; 
end; 
if (dr<tr+s) and (dc>=tc+s) then chessboard(tr,tc+s,dr,dc,s) 
else begin board[tr+s-1][tc+s]:=t; 
______chessboard(tr,tc,tr+s-1,tc+s-1,s)______; end; 
if (dr>=tr+s) and (dc<tc+s) then chessboard(tr+s,tc+s,dr,dc,s) else begin 
board[tr+s][tc+s]:=t; 
______chessboard(tr,tc+s,tr+s-1,tc+s,s)______; end; 
if (dr>=tr+s) and (dc>=tc+s) then chessboard(tr+s,tc+s,dr,dc,s) 
else begin board[tr+s][tc+s]:=t; 
_____chessboard(tr+s,tc,tr+s,tc+s-1,s)______; end; 
end; 
procedure prt1(n:integer); 
var I,j:integer; 
begin 
for I:=1 to n do begin 
for j:=1 to n do write(board[i][j]:3); 
writeln; 
end; 
end; 
begin 
writeln(‘input size(4/8/16/64):’); 
readln(size); writeln(‘input the position of special block(x,y):’); 
readln(dr,dc); board[dr][dc]:=-1; 
tile:=1; chessboard(1,1,dr,dc,size); prt1(size); 
end.