概率与期望

[期望 博客](https://www.luogu.com.cn/blog/ShineEternal/mathematical-expectation) [概率DP/期望DP总结](https://blog.csdn.net/myjs999/article/details/81022546?ops_request_misc=%257B%2522request%255Fid%2522%253A%2522161614237916780255210398%2522%252C%2522scm%2522%253A%252220140713.130102334..%2522%257D&request_id=161614237916780255210398&biz_id=0&utm_medium=distribute.pc_search_result.none-task-blog-2~all~baidu_landing_v2~default-6-81022546.first_rank_v2_pc_rank_v29&utm_term=概率DP) [常见分布 的 数学期望以及方差公式](https://blog.csdn.net/sodacoco/article/details/89041910?ops_request_misc=%257B%2522request%255Fid%2522%253A%2522161597104816780255257723%2522%252C%2522scm%2522%253A%252220140713.130102334..%2522%257D&request_id=161597104816780255257723&biz_id=0&utm_medium=distribute.pc_search_result.none-task-blog-2~all~sobaiduend~default-1-89041910.pc_search_result_cache&utm_term=%E6%9C%9F%E6%9C%9B%E5%85%AC%E5%BC%8F)------ [方差（补充）](https://blog.csdn.net/qq_43410618/article/details/105652350?ops_request_misc=%257B%2522request%255Fid%2522%253A%2522161561703716780265459657%2522%252C%2522scm%2522%253A%252220140713.130102334..%2522%257D&request_id=161561703716780265459657&biz_id=0&utm_medium=distribute.pc_search_result.none-task-blog-2~all~sobaiduend~default-1-105652350.pc_search_result_no_baidu_js&utm_term=方差的计算公式) [P4316 绿豆蛙的归宿](https://www.luogu.com.cn/problem/P4316)：按照拓扑序逆推，最终答案是dp[1]。 对于求期望的题，可以考虑每个独立事件的期望，然后相加。例如[P1297 [国家集训队]单选错位](https://www.luogu.com.cn/problem/P1297)，可分别考虑每道题做对的概率，然后相加。因为此时Xi=1，所以  [P1850 [NOIP2016 提高组] 换教室](https://www.luogu.com.cn/problem/P1850)：~~神仙dp~~。注意dis和dp数组的初始化，最终答案是换0~m次教室的答案期望的最小值。 [P1654 OSU!](https://www.luogu.com.cn/problem/P1654)较[P1365 WJMZBMR打osu! / Easy](https://www.luogu.com.cn/problem/P1365)更为一般化，一次的和二次的要分开算，拓展到n次应该也好做。