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On Thu, Nov 04, 2010 at 10:50:06AM -0700, michael rice wrote:
> Hi, > > I've been looking at a "flagstone problem," where no two adjacent > n-tuples can be identical. I solved the problem with Icon using Interesting stuff! > > ========= Here's my Haskell code ======== > > import Data.Bits > import Data.List > > flagstone n = foldl (++) "" (take n (map show (f $ group [if even y > then 0 else 1 | y <- [bitcount x | x <- [20..]]]))) By the way, I would write this as flagstone n = concat . take n . map show . f . group . map (fromEnum . odd . bitcount) $ [20..] You should never use foldl (++) as it is rather inefficient: you get things like (((a ++ b) ++ c) ++ d) ... which ends up traversing the left part of the list repeatedly. And list comprehensions can be nice at times, but personally using map seems clearer in this case. > ========= My question ======== > > A further exercise in the text: > > "Exercise 5.-(a) Define a(n) as the sum of the binary > digits in the binary representation of n. Define b(i) as > the number of a's between successive zeros as before. > Then T = b(1) b(2) b(3) b(4) ... gives an infinite > sequence of *seven* symbols with no repeats. (b) Write > a routine to generate a sequence for seven colors of > beads on a string with no repeats." > > I may be misreading, but does this make any sense? Doesn't make much sense to me. The sum of binary digits in the binary representation of n will not be zero very often... -Brent _______________________________________________ Haskell-Cafe mailing list [hidden email] http://www.haskell.org/mailman/listinfo/haskell-cafe |
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In reply to this post by Brent Yorgey-2
On Nov 6, 2010, at 4:03 AM, Brent Yorgey wrote: > Doesn't make much sense to me. The sum of binary digits in the binary > representation of n will not be zero very often... I think they mean "the sum (mod 2)" when they say "the sum of binary digits". That should be zero "half" the time. _______________________________________________ Haskell-Cafe mailing list [hidden email] http://www.haskell.org/mailman/listinfo/haskell-cafe |
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