Alice and Bob are playing a simple game. They line up a row of n identical coins, all with the heads facing down onto the table and the tails upward. For exactly mm times they select any k of the coins and toss them into the air, replacing each of th…

题目链接:https://www.jisuanke.com/contest/2870?view=challenges 题目大意:给出n个都正面朝下的硬币,操作m次,每次都选取k枚硬币抛到空中,求操作m次后,硬币向上的期望值. 思路: 1.期望跟概率还是有点不同的,期望要枚举出抛的所有的情况,然后求sigma(i * dp[][]) 2.dp[i][j]表示进行i次操作后,有j枚硬币向上的概率.这样就可以求最后的硬币向上的期望了. 3.值得注意的是,预处理的组合数要开 double 型. 代码:…

Alice and Bob are playing a simple game. They line up a row of nn identical coins, all with the heads facing down onto the table and the tails upward. For exactly mm times they select any kk of the coins and toss them into the air, replacing each of…

I. Older Brother Your older brother is an amateur mathematician with lots of experience. However, his memory is very bad. He recently got interested in linear algebra over finite fields, but he does not remember exactly which finite fields exist. For…

L. Sticky Situation While on summer camp, you are playing a game of hide-and-seek in the forest. You need to designate a “safe zone”, where, if the players manage to sneak there without being detected,they beat the seeker. It is therefore of utmost i…

All as we know, a mountain is a large landform that stretches above the surrounding land in a limited area. If we as the tourists take a picture of a distant mountain and print it out, the image on the surface of paper will be in the shape of a parti…

题目链接:Coins Description Alice and Bob are playing a simple game. They line up a row of nn identical coins, all with the heads facing down onto the table and the tails upward. For exactly mm times they select any kk of the coins and toss them into the…

挺不错的概率DP,看似基础,实则很考验扎实的功底 这题很明显是个DP,为什么???找规律或者算组合数这种概率,N不可能给的这么友善... 因为DP一般都要在支持N^2操作嘛. 稍微理解一下,这DP[i][j]还是不好想啊,首先是写DP[I][j]的含义 首先我们想这道题是要求一个最优决策下的期望,那么这个我们的最优决策是什么??? 决策就是:我们假设我这一次需要翻转K个硬币,我们不愿翻那些已经在正面的,而去翻那些没有在正面的 而如果剩余的反面的不足,我再去翻转正面的 那么给dp[i][j]一个含…

A. Coins Alice and Bob are playing a simple game. They line up a row of nnn identical coins, all with the heads facing down onto the table and the tails upward. For exactly mmm times they select any kkk of the coins and toss them into the air, replac…

Daydreaming Stockbroker Gina Reed, the famous stockbroker, is having a slow day at work, and between rounds of solitaire she is day-dreaming. Foretelling the future is hard, but imagine if you could just go back in time and use your knowledge of stoc…