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C. Dancing Lessons There are n people taking dancing lessons. Every person is characterized by his/her dancing skill ai. At the beginning of the lesso 阅读全文
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E. George and Cards George is a cat, so he loves playing very much. Vitaly put n cards in a row in front of George. Each card has one integer written 阅读全文
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Lanterns Problem Description Alice has received a beautiful present from Bob. The present contains n lanterns and m switches. Each switch controls som 阅读全文
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275. To xor or not to xor 275. To xor or not to xor The sequence of non-negative integers A1, A2, ..., AN is given. You are to find some subsequence A 阅读全文
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Countries 描述 There are two antagonistic countries, country A and country B. They are in a war, and keep launching missiles towards each other. It is k 阅读全文
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考研路茫茫——空调教室 Problem Description 众所周知，HDU的考研教室是没有空调的，于是就苦了不少不去图书馆的考研仔们。Lele也是其中一个。而某教室旁边又摆着两个未装上的空调，更是引起人们无限YY。一个炎热的下午，Lele照例在教室睡觉的时候，竟然做起了空调教室的美梦。Lele 阅读全文
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D. Acyclic Organic Compounds You are given a tree T with n vertices (numbered 1 through n) and a letter in each vertex. The tree is rooted at vertex 1 阅读全文
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D. Fools and Foolproof Roads You must have heard all about the Foolland on your Geography lessons. Specifically, you must know that federal structure 阅读全文
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B2. Shave Beaver! The Smart Beaver has recently designed and built an innovative nanotechnologic all-purpose beaver mass shaving machine, "Beavershave 阅读全文
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Jewel Problem Description Jimmy wants to make a special necklace for his girlfriend. He bought many beads with various sizes, and no two beads are wit 阅读全文