谁有《全国信息学奥林匹克联赛 培训教程（二）的课后习题的答案？

[参考程序]
program fourcolor;
const num=20;
var a:array [1..num,1..num] of 0..1;
s:array [1..num] of 0..4; {用1-4分别代表RBWY四种颜色;0代表末填进任何颜色}
k1,k2,n:integer;

function pd(i,j:integer):boolean;{判断可行性：第I个省填上第J种颜色}
var k:integer;
begin
for k:=1 to i-1 do
if (a[i,k]=1) and (j=s[k]) {省I和省J相邻且将填进的颜色和已有的颜色相同}
then begin pd:=false; exit; end;
pd:=true;
end;

procedure print;{打印结果}
var k:integer;
begin
for k:=1 to n do{将数字转为RBWY串}
case s[k] of
1:write('R':4);
2:write('B':4);
3:write('W':4);
4:write('Y':4);
end;
writeln;
end;

procedure try(i:integer);
var j:integer;
begin
for j:=1 to 4 do
if pd(i,j) then begin
s[i]:=j;
if i=n then print
else