From 09351d4e857b376c2affd5b13d90280ca72a9112 Mon Sep 17 00:00:00 2001
From: Mohammad S Anwar <mohammad.anwar@yahoo.com>
Date: Wed, 2 Dec 2020 22:17:45 +0000
Subject: - Added Haskell solution by Ulrich Rieke.

---
 challenge-089/ulrich-rieke/haskell/ch-2.hs | 45 ++++++++++++++++++++++++++++++
 1 file changed, 45 insertions(+)
 create mode 100644 challenge-089/ulrich-rieke/haskell/ch-2.hs

diff --git a/challenge-089/ulrich-rieke/haskell/ch-2.hs b/challenge-089/ulrich-rieke/haskell/ch-2.hs
new file mode 100644
index 0000000000..47ae1f3d45
--- /dev/null
+++ b/challenge-089/ulrich-rieke/haskell/ch-2.hs
@@ -0,0 +1,45 @@
+module Challenge089_2
+  where
+import Data.List ( (!!) )
+import Data.List.Split ( chunksOf )
+
+count :: Eq a => a -> [a] -> Int
+count c [] = 0
+count d (x:xs)
+  |d == x = 1 + count d xs
+  |otherwise = count d xs
+
+--find all lists that fulfill the sum conditions, in a list comprehension
+possibleLists :: [[Int]]
+possibleLists = [[a , b , c , d , e , f , g , h , i] | a <- [1 .. 9] ,
+b <- [1 .. 9], c <- [1 .. 9] , d <- [1 .. 9], e <- [1 .. 9] , f <- [1 .. 9],
+g <- [1 .. 9], h <- [1 .. 9], i <- [1 .. 9] ,
+a + b + c == 15, d + e + f == 15 , g + h + i == 15,
+a + d + g == 15 , b + e + h == 15 , c + f + i == 15 , a + e + i == 15 ,
+c + e + g == 15]
+
+--in all possible lists find those where every number occurs only once
+validLists :: [[Int]]
+validLists = filter myCondition possibleLists
+  where
+    myCondition :: [Int] -> Bool
+    myCondition sublist =  all ( 1 == ) $ map (\n -> count n sublist )
+      sublist
+
+--convert a row of 3 numbers into a string
+convertRow :: [Int] -> String
+convertRow row = "[ " ++ (show $ row !! 0 ) ++ " " ++ ( show $ row !! 1 )
+++ " " ++ ( show $ row !! 2 ) ++ " ]"
+
+--convert three rows of 3 numbers each into a "magic square"
+--first, convert each row to a string, and then print that string
+--after the 3rd row of the square add an empty line
+printSquare :: [Int] -> IO ( )
+printSquare magic = do
+  let rows = map convertRow $ chunksOf 3 magic
+  mapM_ putStrLn rows
+  putStrLn "  "
+
+main :: IO ( )
+main = do
+  mapM_ printSquare validLists
-- 
cgit