Re: [Haskell-beginners] Project euler question

Am 05/21/2014 11:14 PM, schrieb David McBride:

Err actually I guess I got the euler answer, I guess I don't understand your solution without the "minus" function definition.

"minus" is from Data.List.Ordered. It it like the standard set operation "minus" when both lists are ordered.

On Wed, May 21, 2014 at 5:10 PM, David McBride mailto:toad3k@gmail.com> wrote:

For what it is worth, I'm getting the same answer as you are.

> head $ drop (1000000-1) $ sort $ Data.List.permutations [0..9] [2,7,8,3,9,1,5,4,6,0]

>(sort $ Data.List.permutations [0..9]) !! (1000000-1) [2,7,8,3,9,1,5,4,6,0]

I guess either euler is wrong or we are both crazy.

On Wed, May 21, 2014 at 4:09 PM, martin mailto:martin.drautzburg@web.de> wrote:

Hello all,

I tried to solve Problem 24 (https://projecteuler.net/problem=24) and came up with the following solution:

import Data.List.Ordered import Data.Char

elems = [0,1,2,3,4,5,6,7,8,9] :: [Int]

x = do a <- elems b <- elems `without` [a] c <- elems `without` [a,b] d <- elems `without` [a,b,c] e <- elems `without` [a,b,c,d] f <- elems `without` [a,b,c,d,e] g <- elems `without` [a,b,c,d,e,f] h <- elems `without` [a,b,c,d,e,f,g] i <- elems `without` [a,b,c,d,e,f,g,h] j <- elems `without` [a,b,c,d,e,f,g,h,i] return [a,b,c,d,e,f,g,h,i,j]

without a b = minus a ( sort b)

solution = filter isDigit $ show $ (x !! 1000001) -- "2783915640"

PE tells me that this is wrong, and I peeked the correct answer, which is 2783915460 (the 4 and 6 are swapped). So I tried to find out where the correct answer is in my list x and added

y = filter (\(x,y) -> x == "2783915460") $ zip (map (filter isDigit . show) x) [1..] -- [("2783915460",1000000)]

How can that be? "solution" tells me that the millionth element is "2783915640" but "y" tells me that "2783915460" is at the millionth position? I just cannot see it.

_______________________________________________ Beginners mailing list Beginners@haskell.org mailto:Beginners@haskell.org http://www.haskell.org/mailman/listinfo/beginners

_______________________________________________ Beginners mailing list Beginners@haskell.org http://www.haskell.org/mailman/listinfo/beginners