摘要：
There are n numbers 3^0, 3^1, . . . , 3^n-1. Each time you can choose a subset of them (may be empty), and then add them up. Count how many numbers ca 阅读全文
摘要：
Senior Pan fails in his discrete math exam again. So he asks Master ZKC to give him graph theory problems everyday. The task is simple : ZKC will give 阅读全文