rt

https://www.luogu.com.cn/blog/dnjqxopx/solution-323 这篇证明缺失

&

https://www.luogu.com.cn/blog/pigeon-team/solution-p4136 这篇证明缺失

&

https://www.luogu.com.cn/blog/cmkun/solution-p4136 这篇啥也不是