Re: [Haskell-beginners] Project euler question

Err actually I guess I got the euler answer, I guess I don't understand your solution without the "minus" function definition. On Wed, May 21, 2014 at 5:10 PM, David McBride 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 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.

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