5159：Card

Special Judge 特殊评判

题目描述

There are x cards on the desk, they are numbered from 1 to x. The score of the card which is numbered i(1<=i<=x) is i. Every round BieBie picks one card out of the x cards，then puts it back. He does the same operation for b rounds. Assume that the score of the j-th card he picks is ${{\rm{S}}_{\rm{j}}}$ . You are expected to calculate the expectation of the sum of the different score he picks.

输入解释

Multi test cases，the first line of the input is a number T which indicates the number of test cases.
In the next T lines, every line contain x,b separated by exactly one space.

[Technique specification]
All numbers are integers.
1<=T<=500000
1<=x<=100000
1<=b<=5

输出解释

Each case occupies one line. The output format is Case #id: ans, here id is the data number which starts from 1，ans is the expectation, accurate to 3 decimal places.
See the sample for more details.

输入样例

2
2 3
3 3

输出样例

Case #1: 2.625
Case #2: 4.222

提示

For the first case, all possible combinations BieBie can pick are (1, 1, 1),(1,1,2),(1,2,1),(1,2,2),(2,1,1),(2,1,2),(2,2,1),(2,2,2)
For (1,1,1),there is only one kind number i.e. 1, so the sum of different score is 1.
However, for (1,2,1), there are two kind numbers i.e. 1 and 2, so the sum of different score is 1+2=3.
So the sums of different score to corresponding combination are 1，3，3，3，3，3，3，2
So the expectation is (1+3+3+3+3+3+3+2)/8=2.625

来自杭电HDUOJ的附加信息

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heyang

该题目是Virtual Judge题目，来自杭电HDUOJ

题目来源 BestCoder Round #26

源链接： HDU-5159

最后修改于 2020-10-25T23:20:17+00:00 由爬虫自动更新

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通过率 --%

时间上限	内存上限
10000/5000MS(Java/Others)	32768/32768K(Java/Others)