Euler questions 5/6

src/projectEuler/question5.hs

@@ -0,0 +1,65 @@
+import           Data.Set    (fromList)
+import           Debug.Trace (trace)
+
+{-
+  https://projecteuler.net/problem=5
+
+  2520 is the smallest number that can be divided by each of the numbers from 1 to 10 without any remainder.
+  What is the smallest positive number that is evenly divisible by all of the numbers from 1 to 20?
+-}
+
+wrong = map (`div` 2520) [1..10]
+-- [0,0,0,0,0,0,0,0,0,0]
+
+_2520misleadingSolution = map (2520 `div`) [1..10]
+-- [2520,1260,840,630,504,420,360,315,280,252]
+
+_2520correctSolution = map (2520 /) [1..10]
+-- [2520.0,1260.0,840.0,630.0,504.0,420.0,360.0,315.0,280.0,252.0]
+
+-- sieve method
+-- zip 20 lists together
+
+even' n = n `rem` 2 == 0
+odd' = not . even'
+
+multipleOf x n = {- trace ("x:" <> show x <> ", n:" <> show n) $ -} n `rem` x == 0
+
+threven = multipleOf 3
+fouevn = multipleOf 4
+fiven = multipleOf 5
+
+{-
+filter even [1..100]
+filter fouevn $ filter threven $ filter even [1..100]
+
+-- :t foldl (\b a -> undefined) [] [1..]
+foldl (\b a -> undefined) [] [1..]
+-}
+
+bruteForce =
+  filter (multipleOf 20) $
+  filter (multipleOf 19) $
+  filter (multipleOf 18) $
+  filter (multipleOf 17) $
+  filter (multipleOf 16) $
+  filter (multipleOf 15) $
+  filter (multipleOf 14) $
+  filter (multipleOf 13) $
+  filter (multipleOf 12) $
+  filter (multipleOf 11) $
+  filter (multipleOf 10) $
+  filter (multipleOf  9) $
+  filter (multipleOf  8) $
+  filter (multipleOf  7) $
+  filter (multipleOf  6) $
+  filter (multipleOf  5) $
+  filter (multipleOf  4) $
+  filter (multipleOf  3) $
+  filter (multipleOf  2) [232792550..]
+-- answer is 232792560
+
+test = map (filter . multipleOf) [1..10]
+
+-- lol
+solve = foldl1 lcm [1..20]

src/projectEuler/question6.hs

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+{-
+The sum of the squares of the first ten natural numbers is,
+  1^2 + 2^2 + ... + 10^2 = 385
+
+The square of the sum of the first ten natural numbers is,
+  (1 + 2 + ... + 10)^2 = 55^2 = 3025
+
+Hence the difference between the sum of the squares
+  of the first ten natural numbers and the square
+  of the sum is 3025 - 385 = 2640
+
+Find the difference between the sum of the squares
+  of the first one hundred natural numbers
+  and the square of the sum.
+-}
+upperRange = 100
+square n = n^2
+squares = map square [1..upperRange]
+sum' = go 0
+  where
+    go acc []     = acc
+    go acc (x:xs) = go (acc+x) xs
+
+sumOfSquares = sum' squares
+
+squareOfTheSum = (sum [1..upperRange])^2
+
+solution = squareOfTheSum - sumOfSquares