Data commit

Task/Taxicab-numbers/Haskell/taxicab-numbers.hs

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+import Data.List (groupBy, sortOn, tails, transpose)
+import Data.Function (on)
+
+--------------------- TAXICAB NUMBERS --------------------
+
+taxis :: Int -> [[(Int, ((Int, Int), (Int, Int)))]]
+taxis nCubes =
+  filter ((> 1) . length) $
+  groupBy (on (==) fst) $
+  sortOn fst
+    [ (fst x + fst y, (x, y))
+    | (x:t) <- tails $ ((^ 3) >>= (,)) <$> [1 .. nCubes]
+    , y <- t ]
+
+--------------------------- TEST -------------------------
+main :: IO ()
+main =
+  mapM_ putStrLn $
+  concat <$>
+  transpose
+    (((<$>) =<< flip justifyRight ' ' . maximum . (length <$>)) <$>
+     transpose (taxiRow <$> (take 25 xs <> take 7 (drop 1999 xs))))
+  where
+    xs = zip [1 ..] (taxis 1200)
+    justifyRight n c = (drop . length) <*> (replicate n c <>)
+
+------------------------- DISPLAY ------------------------
+taxiRow :: (Int, [(Int, ((Int, Int), (Int, Int)))]) -> [String]
+taxiRow (n, [(a, ((axc, axr), (ayc, ayr))), (b, ((bxc, bxr), (byc, byr)))]) =
+  concat
+    [ [show n, ". ", show a, " = "]
+    , term axr axc " + "
+    , term ayr ayc "  or  "
+    , term bxr bxc " + "
+    , term byr byc []
+    ]
+  where
+    term r c l = ["(", show r, "^3=", show c, ")", l]