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竟然进第一页了……这辈子值了，附关键优化方法

Posted by sweetsc at 2009-06-24 22:49:40 on Problem 2992 and last updated at 2009-06-24 22:53:33 
还是要预处理C（n，k），然后直接输出的……
预处理时，C（n,k）和c（n，k+1）有递推关系，C（n，k+1）=C(n,k)/(k+1)*(n-k)
利用这个就不TLE了……
可见数学有用啊……
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