数据生成器
```cpp
void build(int n)
{
cout<<2*n+1<<endl;
for(int i=n;i>=1;++i)
cout<<i<<" ";
cout<<n+1<<" ";
for(int i=n;i>=1;--i)
cout<<i+n+1<<" ";
}
```
输出一律应为
```
3
1
1
```
by ZhuMingYang @ 2020-07-24 17:02:57
@[chen_zhe](/user/8457)
by Spasmodic @ 2020-08-09 13:30:30