2012 年 8月 7 日随笔档案 - hebozi

组合数的奇偶性

摘要：组合数的奇偶性08年安徽高中联赛的初赛题中有这么一题：多项式(1+x)^2008=a0+a1x+……+a2008x^2008,系数a1,a2,……,a2008中共有多少个偶数。（ans=2008-128=1881）看到这题，想到的就是判断c(2008,k)的奇偶性，由于没有相关知识基础就去搜了下资料。（附下）但是如何运用呢？这里似乎涉及到一点位运算的知识。10进制（2008）=2进制（11111011000）由结论：对于C(n,k),若n&k == k 则c(n,k)为奇数，否则为偶数。于是开始匹配。2008：1 1 1 1 1 0 1 1 0 0 0 0 -->0 1 0 0 阅读全文

posted @ 2012-08-07 21:37 hebozi 阅读(566) 评论(0) 推荐(0)

HDU 4341 Gold miner 分组背包

摘要： Gold minerTime Limit: 4000/2000 MS (Java/Others)Memory Limit: 32768/32768 K (Java/Others)Total Submission(s): 132Accepted Submission(s): 74Problem DescriptionHomelesser likes playing Gold miners in class. He has to pay much attention to the teacher to avoid being noticed. So he always lose the game. 阅读全文

posted @ 2012-08-07 21:28 hebozi 阅读(298) 评论(0) 推荐(0)

HDU 4349 Xiao Ming's Hope 组合数的奇偶性

摘要： Xiao Ming's HopeTime Limit: 2000/1000 MS (Java/Others)Memory Limit: 32768/32768 K (Java/Others)Total Submission(s): 0Accepted Submission(s): 0Problem DescriptionXiao Ming likes counting numbers very much, especially he is fond of counting odd numbers. Maybe he thinks it is the best way to show h 阅读全文

posted @ 2012-08-07 16:01 hebozi 阅读(225) 评论(0) 推荐(0)

2012年8月7日