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发信人: huhaiming (一生只爱她), 信区: Program
标 题: 1004 Present
发信站: 荔园晨风BBS站 (Sun Jun 8 19:27:56 2003), 站内信件
Present
Time limit: 1 Seconds Memory limit: 32768K
Total Submit: 367 Accepted Submit: 94
There are N friends who has bought one present each. They mix their
presents together and then each person takes one randomly. What is the
probability that exactly M people got their own present.
Input
Each line is one case and contains two integers N (0 < N < 100), M (0 <=
M <= N).
Output
For each case, output the result in one line.
The result are exact to 8 decimal places.
Sample Input
3 1
4 2
Sample Output
0.50000000
0.25000000
Author: ZHANG, Zheng
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菩提本无树，明镜亦非台
本来无一物，何处惹尘埃
※ 修改:·huhaiming 於 Jun 8 20:55:25 修改本文·[FROM: 192.168.0.200]
※ 来源:·荔园晨风BBS站 bbs.szu.edu.cn·[FROM: 192.168.0.200]
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