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PAT 1015. Reversible Primes A reversible prime in any number system is a prime whose "reverse" in that number system is also a prime. For example in t 阅读全文
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PAT 1014. Waiting in Line (30) Suppose a bank has N windows open for service. There is a yellow line in front of the windows which devides the waiting 阅读全文
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Battle Over Cities It is vitally important to have all the cities connected by highways in a war. If a city is occupied by the enemy, all the highways 阅读全文