摘要：
一个包含四个点的完全图，可以在任意节点出发，可以在任意节点结束，给出每个点被经过的次数，求有多少种合法的遍历序列。如果两个序列至少有一位是不同的，则认为它们不相同。 Input Sample Output 题意：给a个A，b个B，c个C，d个D，求有少种排列，使得相邻的两个不同。 思路：用容斥来做， 阅读全文
摘要：
As we know, Rikka is poor at math. Yuta is worrying about this situation, so he gives Rikka some math tasks to practice. There is one of them: Yuta ha 阅读全文
摘要：
A thief made his way to a shop. As usual he has his lucky knapsack with him. The knapsack can contain k objects. There are n kinds of products in the 阅读全文