摘要：描述 There are a group of students. Some of them may know each other, while others don't. For example, A and B know each other, B and C know each other. 阅读全文

摘要：描述 The gopher family, having averted the canine threat, must face a new predator. The are n gophers and m gopher holes, each at distinct (x, y) coordi 阅读全文