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Re:雁过留声——排列组合和dp

Posted by zzsx65zdf at 2012-03-30 19:36:32 on Problem 3718
In Reply To:雁过留声——排列组合和dp Posted by:fanhqme at 2009-10-05 21:45:44 
f(m,k)=(
f(m-1,k-3)*c(k,3)*c(n-k,0)+
f(m-1,k+3)*c(k,0)*c(n-k,3)+
f(m-1,k+1)*c(k,1)*c(n-k,2)+
f(m-1,k-1)*c(k,2)*c(n-k,1)-
f(m-2,k)*(c(n,3)-m+2))/m
神犇给的转移方程留了一点小错误给我们
应该是这样的
f(m,k)=(
f(m-1,k-3)*c(k,3)*c(n-k,0)+
f(m-1,k+3)*c(k,0)*c(n-k,3)+
f(m-1,k+1)*c(k,1)*c(n-k,2)+
f(m-1,k-1)*c(k,2)*c(n-k,1)-
f(m-2,k)*（m-1)*(c(n,3)-m+2))/m
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