golf.hs

golf.hs

-- Outputs the number of strings of length six with the digits 0-9 with only two numbers used
-- (e.a. "100110", "611661", "899889") in 119 characters of Haskell. Enjoy!

import Data.List
z x|length x<6=z("0"++x)|length x==6=x
main=print$length$filter((==2).length)$map(nub.z.show)[0..999999]

ungolf.hs

import Data.List -- for nub

-- Converts integers into a string of six digits
sixstring :: Int -> String
sixstring x = zeroes (show x)

-- Helper function, appends zeroes to a string of digits until
-- the length of the string is 6.
zeroes :: String -> String
zeroes x | length x < 6 = zeroes ("0"++x) 
         | length x == 6 = x

-- Returns true if the set of unique characters used in the string
-- passed is exactly two.
exactlyTwoNumbers :: String -> Bool
exactlyTwoNumbers x = length (nub x) == 2

-- Count the number of strings from 000000 to 999999 with exactly
-- two digits used.
n = length $ filter exactlyTwoNumbers $ map sixstring [0..999999]

main = print n