dmalikov

import Control.Monad (replicateM, join)
import Data.List (nub, sort, group)
import Control.Arrow ((&&&), (***))
import Numeric (showFFloat)

allVariantsNumber :: Integer
allVariantsNumber = 4^9 * 6^6

groupVariants :: [[Integer]] -> [(Integer,Integer)]
groupVariants = map ((&&&) head (toInteger . length)) . group . sort . map sum

dmalikov

import Data.List (nub, sort)
import Data.Numbers.Primes
import Control.Arrow ((&&&))

radical :: Integer -> Integer
radical = product . nub . primeFactors

radicalsSortedBelow :: Integer -> [Integer]
radicalsSortedBelow = map snd . sort . map ((&&&) radical id) . enumFromTo 1

dmalikov

import Roman
import System.Environment
import Data.Char (toUpper)
import Control.Arrow ((&&&))

redundantChars :: String -> Int
redundantChars = (\(x,y) -> length x - length y) . (id &&& (toRoman . fromRoman))

main = do
    romans <- getContents

dmalikov

moddule = 10 ^ 8
lastDigits x = x `mod` moddule

fastPow :: Integer -> Integer -> Integer -> Integer
fastPow base 1 m = mod base m 
fastPow base pow m | even pow = mod ((fastPow base (div pow 2) m) ^ 2) m
                   | odd  pow = mod ((fastPow base (div (pow-1) 2) m) ^ 2 * base) m
                   
tetration a 1 = lastDigits a
tetration a k = lastDigits ( fastPow a' (tetration a' k') moddule)

dmalikov

import Data.Numbers.Primes

semiPrime :: Int -> Bool
semiPrime list = 2 == (length $ primeFactors list)

semiPrimesBelow :: Int -> Int
semiPrimesBelow n = length $ filter semiPrime [1..n-1]

main = putStrLn $ show $ semiPrimesBelow (10^8)