hust2015暑假集训 0713 A a dangerous tripJul 13, 2015·251 words·1 minACM HUSThttp://acm.hust.edu.cn/vjudge/contest/view.action?cid=82557#problem/A Zk的解法：拆点，把每一个点存成两份，r[i]和r[n+i]