数学期望 P=Σ每一种状态*对应的概率。 因为不可能枚举完所有的状态，有时也不可能枚举完，比如抛硬币，有可能一直是正面，etc。在没有接触数学期望时看到数学期望的题可能会觉得很阔怕（因为我高中就是这么认为的，对不起何老板了QwQ），避之不及。 但是现在发现大多数题就是手动找公式或者DP推出即可，只要 ...
分类：
其他好文 时间：
2018-01-01 11:41:38
阅读次数：
259
King Arthur is an narcissist who intends to spare no coins to celebrate his coming K-th birthday. The luxurious celebration will start on his birthday ...
分类：
其他好文 时间：
2017-12-17 15:03:02
阅读次数：
189
The dragon and the princess are arguing about what to do on the New Year's Eve. The dragon suggests flying to the mountains to watch fairies dancing i ...
分类：
其他好文 时间：
2017-12-15 22:36:13
阅读次数：
146
BuggyD loves to carry his favorite die around. Perhaps you wonder why it's his favorite? Well, his die is magical and can be transformed into an N-sid ...
分类：
其他好文 时间：
2017-12-15 15:08:26
阅读次数：
371
There is a very simple and interesting one-person game. You have 3 dice, namely Die1, Die2 and Die3. Die1 has K1 faces. Die2 has K2 faces. Die3 has K3 ...
分类：
其他好文 时间：
2017-12-15 13:33:53
阅读次数：
136
In 0th day, there are n-1 people and 1 bloodsucker. Every day, two and only two of them meet. Nothing will happen if they are of the same species, tha ...
分类：
其他好文 时间：
2017-12-15 11:11:21
阅读次数：
141
问题： Ivan is fond of collecting. Unlike other people who collect post stamps, coins or other material stuff, he collects software bugs. When Ivan gets ...
分类：
其他好文 时间：
2017-12-08 13:51:53
阅读次数：
212
问题： You live in a village but work in another village. You decided to follow the straight path between your house (A) and the working place (B), but t ...
分类：
其他好文 时间：
2017-12-08 12:18:41
阅读次数：
223
啊 我永远喜欢期望题 "BZOJ 3143" 游走 题意 有一个n个点m条边的无向联通图，每条边按1~m编号，从1号点出发，每次随机选择与当前点相连的一条边，走到这条边的另一个端点，一旦走到n号节点就停下。每经过一条边，要付出这条边的编号这么多的代价。现将所有边用1~m重新编号，使总代价的期望最小， ...
分类：
其他好文 时间：
2017-12-07 13:26:46
阅读次数：
162
