摘要：Polycarpus has n friends in Tarasov city. Polycarpus knows phone numbers of all his friends: they are strings s1,s2,...,sn. All these strings consist 阅读全文

摘要：One cold winter evening Alice and her older brother Bob was sitting at home near the fireplace and giving each other interesting problems to solve. Wh 阅读全文

摘要：Petr stands in line of n people, but he doesn't know exactly which position he occupies. He can say that there are no less than a people standing in f 阅读全文