[Haskell-beginners] Project euler question

[David McBride]

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 <toad3k at 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 <martin.drautzburg at 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.
>>
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>
>
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