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Re:为什么啊??

Posted by bbo at 2009-04-18 10:54:34 on Problem 3219
In Reply To:为什么啊?? Posted by:zjut020 at 2009-02-27 19:27:25

n! / (k! (n - k)!) 判断分子和分母的2的阶数大小即可
而且计算N！中2的阶数，只要计算N/2+N/4……
但如果用N/2+N/4……，这样的效率还是很低，用移位操作比较好
与        while(n=n>>1) a+=n;
         while(m=m>>1) b+=m;
         while(k=k>>1) c+=k;
等价的，
我也从这题中学到很多，呵呵，共同进步...

Followed by:

谢谢！ (5) zjut020 2009-08-08 21:29:43
还记得统计阶乘中因子3/5/7...的个数么? (29) tzkq 2010-07-30 03:57:12

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