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