摘要：
Starting a Scenic Railroad Service 题目描述 Jim, working for a railroad company, is responsible for planning a new tourist train service. He is sure that 阅读全文
摘要：
Rendezvous on a Tetrahedron 题目描述 One day, you found two worms P and Q crawling on the surface of a regular tetrahedron with four vertices A, B, C, and 阅读全文