5194：DZY Loves Balls

题目描述

There are $n$ black balls and $m$ white balls in the big box.

Now, DZY starts to randomly pick out the balls one by one. It forms a sequence $S$. If at the $i$-th operation, DZY takes out the black ball, $S_i=1$, otherwise $S_i=0$.

DZY wants to know the expected times that '01' occurs in $S$.

输入解释

The input consists several test cases. ($TestCase\leq 150$)

The first line contains two integers, $n$, $m(1\leq n,m\leq 12)$

输出解释

For each case, output the corresponding result, the format is $p/q$($p$ and $q$ are coprime)

输入样例

1 1
2 3

输出样例

1/2
6/5

提示

Case 1: S='01' or S='10', so the expected times = 1/2 = 1/2
Case 2: S='00011' or S='00101' or S='00110' or S='01001' or S='01010' 
or S='01100' or S='10001' or S='10010' or S='10100' or S='11000',
so the expected times = (1+2+1+2+2+1+1+1+1+0)/10 = 12/10 = 6/5

来自杭电HDUOJ的附加信息

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该题目是Virtual Judge题目，来自杭电HDUOJ

题目来源 BestCoder Round #35

源链接： HDU-5194

最后修改于 2020-10-25T23:20:36+00:00 由爬虫自动更新

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通过率 --%

时间上限	内存上限
2000/1000MS(Java/Others)	65536/65536K(Java/Others)