是 $2^n$ 个国家
by XL4453 @ 2021-11-05 21:37:48
把
for (int i=1,a;i<=n<<1;++i){
改成：
for (int i=1,a;i<=1<<n;++i){
就过了
by XL4453 @ 2021-11-05 21:38:51
@[q_james_c](/user/396789)
by XL4453 @ 2021-11-05 21:39:01
粗心了 多谢！！
by q_james_c @ 2021-11-05 22:27:05