一道pascal题目排列(permutation)【源程序名】permutation.(pas/cpp)【问题描述】有n

很简单,用深度优先搜索,我没做优化,当n=9,r=9时,需要一定时间.
var
n,r,k:byte;
f:array [1..9] of boolean;
a:array [1..9] of byte;
procedure permutation(i:byte);
var j:byte;
begin
if i=r+1 then
begin
for k:=1 to r-1 do
write(a[k],' ');
writeln(a[r]);
exit;
end;
for j:=1 to n do
if f[j] then
begin
f[j]:=false;
a[i]:=j;
permutation(i+1);
f[j]:=true;
end;
end;
begin
fillchar(f,sizeof(f),true);
readln(n);
readln(r);
permutation(1);
end.