https://www.luogu.com.cn/problem/AT_joisc2011_ufo5 https://www.luogu.com.cn/problem/AT_joisc2011_ufo4 https://www.luogu.com.cn/problem/AT_joisc2011_ufo3 https://www.luogu.com.cn/problem/AT_joisc2011_ufo2 https://www.luogu.com.cn/problem/AT_joisc2011_ufo1

这几道题题目都一样，申请删题。