Codeforces Round #437 (Div. 1) C

传送门

题意：一个游戏一共有n个关卡，对于第i关，用a[i]时间通过的概率为p[i],用b[i]通过的时间为1-p[i]，每通过一关后可以选择继续下一关或者时间清0并从第一关开始，先要求通过所有关卡的时间和不能超过R才算彻底通关，问直到彻底通关位置的游戏时间的期望值为多少

做法：

答案一定是满足递增性质的，那么我们二分答案肯定没毛病呀，另外，这个是个dp，因为他每一关的期望对下一关有影响，所以用dp处理没毛病啊，另外转移方程是什么呢。

动动脑子想一想，如果dp[i][j]代表第i关最后的结果j的期望。

嗨呀，那么dp[i][j]=(dp[i+1][j+f[i]]+f[i])*p[i]/100+(dp[i+1][i+s[i]]+s[i])*(100-p[i])/100了嘛，最后dp[0][0]就为答案了呀。

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