摘要：
Problem 1: Guard Mark [Bill Cooperman, 2014]Farmer John and his herd are playing frisbee. Bessie throws thefrisbee down the field, but it's going stra 阅读全文
摘要：
Walls PROBLEM In a country, great walls have been built in such a way that every great wall connects exactly two towns. The great walls do not cross e 阅读全文