Problem 61

61.hs

@@ -0,0 +1,46 @@
+tri = [round $ n * (n + 1) / 2      | n <- [45..140]] 
+sqr = [round $ n * n                | n <- [32..100]]
+pnt = [round $ n * (3 * n - 1) / 2  | n <- [26..81]]
+hex = [round $ n * (2 * n - 1)      | n <- [23..70]]
+hep = [round $ n * (5 * n - 3) / 2  | n <- [21..63]]
+oct = [round $ n * (3 * n - 2)      | n <- [19..58]]
+
+tip :: Int -> String
+tip n = take 2 $ show n
+
+end :: Int -> String
+end n = drop 2 $ show n 
+
+isCyclic :: Int -> Int -> Bool
+isCyclic x y = end x == tip y
+
+poly = [tri, sqr, pnt, hex, hep]
+cyclics = [(a, b, c, d, e, f) | a <- oct,
+                                i <- [0..4],
+                                b <- poly !! i,
+                                isCyclic a b,
+                                
+                                j <- [0..4],
+                                j /= i,
+                                c <- poly !! j,
+                                isCyclic b c,
+
+                                k <- [0..4],
+                                all (k /=) [i, j],
+                                d <- poly !! k,
+                                isCyclic c d,
+
+                                l <- [0..4],
+                                all (l /=) [i, j, k],
+                                e <- poly !! l,
+                                isCyclic d e,
+
+                                m <- [0..4],
+                                all (m /=) [i, j, k, l],
+                                f <- poly !! m,
+                                isCyclic e f,
+                                isCyclic f a]
+
+main = do print $ head cyclics 
+          print $ let (a, b, c, d, e, f) = head cyclics
+                  in a + b + c + d + e + f