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dbalmain's solution

to Diamond in the PureScript Track

Published at Jul 13 2018 · 0 comments
Instructions
Test suite
Solution

Note:

This solution was written on an old version of Exercism. The tests below might not correspond to the solution code, and the exercise may have changed since this code was written.

The diamond kata takes as its input a letter, and outputs it in a diamond shape. Given a letter, it prints a diamond starting with 'A', with the supplied letter at the widest point.

Requirements

  • The first row contains one 'A'.
  • The last row contains one 'A'.
  • All rows, except the first and last, have exactly two identical letters.
  • All rows have as many trailing spaces as leading spaces. (This might be 0).
  • The diamond is horizontally symmetric.
  • The diamond is vertically symmetric.
  • The diamond has a square shape (width equals height).
  • The letters form a diamond shape.
  • The top half has the letters in ascending order.
  • The bottom half has the letters in descending order.
  • The four corners (containing the spaces) are triangles.

Examples

In the following examples, spaces are indicated by · characters.

Diamond for letter 'A':

A

Diamond for letter 'C':

··A··
·B·B·
C···C
·B·B·
··A··

Diamond for letter 'E':

····A····
···B·B···
··C···C··
·D·····D·
E·······E
·D·····D·
··C···C··
···B·B···
····A····

Source

Seb Rose http://claysnow.co.uk/recycling-tests-in-tdd/

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

Main.purs

module Test.Main where

import Prelude
import Control.Monad.Eff (Eff)
import Control.Monad.Eff.AVar (AVAR)
import Control.Monad.Eff.Console (CONSOLE)
import Test.Unit.Assert as Assert
import Test.Unit (TestSuite, suite, test)
import Test.Unit.Console (TESTOUTPUT)
import Test.Unit.Main (runTest)
import Diamond (rows)

main :: forall eff
  . Eff ( avar :: AVAR
        , console :: CONSOLE
        , testOutput :: TESTOUTPUT
        | eff                     
        )
        Unit
main = runTest suites

suites :: forall e. TestSuite e
suites = do
  suite "Diamond.rows" do

    test "Degenerate case with a single 'A' row" $
      Assert.equal   [ "A"
                     ]
                   (rows 'A')

    test "Degenerate case with no row containing 3 distinct groups of spaces" $
      Assert.equal   [ " A "
                     , "B B"
                     , " A "
                     ]
                   (rows 'B')

    test "Smallest non-degenerate case with odd diamond side length" $
      Assert.equal   [ "  A  "
                     , " B B "
                     , "C   C"
                     , " B B "
                     , "  A  "
                     ]
                   (rows 'C')

    test "Smallest non-degenerate case with even diamond side length" $
      Assert.equal   [ "   A   "
                     , "  B B  "
                     , " C   C "
                     , "D     D"
                     , " C   C "
                     , "  B B  "
                     , "   A   "
                     ]
                   (rows 'D')

    test "Largest possible diamond" $
      Assert.equal   [ "                         A                         "
                     , "                        B B                        "
                     , "                       C   C                       "
                     , "                      D     D                      "
                     , "                     E       E                     "
                     , "                    F         F                    "
                     , "                   G           G                   "
                     , "                  H             H                  "
                     , "                 I               I                 "
                     , "                J                 J                "
                     , "               K                   K               "
                     , "              L                     L              "
                     , "             M                       M             "
                     , "            N                         N            "
                     , "           O                           O           "
                     , "          P                             P          "
                     , "         Q                               Q         "
                     , "        R                                 R        "
                     , "       S                                   S       "
                     , "      T                                     T      "
                     , "     U                                       U     "
                     , "    V                                         V    "
                     , "   W                                           W   "
                     , "  X                                             X  "
                     , " Y                                               Y "
                     , "Z                                                 Z"
                     , " Y                                               Y "
                     , "  X                                             X  "
                     , "   W                                           W   "
                     , "    V                                         V    "
                     , "     U                                       U     "
                     , "      T                                     T      "
                     , "       S                                   S       "
                     , "        R                                 R        "
                     , "         Q                               Q         "
                     , "          P                             P          "
                     , "           O                           O           "
                     , "            N                         N            "
                     , "             M                       M             "
                     , "              L                     L              "
                     , "               K                   K               "
                     , "                J                 J                "
                     , "                 I               I                 "
                     , "                  H             H                  "
                     , "                   G           G                   "
                     , "                    F         F                    "
                     , "                     E       E                     "
                     , "                      D     D                      "
                     , "                       C   C                       "
                     , "                        B B                        "
                     , "                         A                         "
                     ]
                   (rows 'Z')
module Diamond
   (rows
   ) where

import Data.Array (drop, replicate, reverse, (..))
import Data.Char (fromCharCode, toCharCode)
import Data.String (fromCharArray)
import Prelude (map, ($), (+), (-), (<>))

rows ∷ Char → Array String
rows c = mirror $ map row (0 .. n)
  where 
    n = toCharCode c - toCharCode 'A'
    char i = fromCharCode $ toCharCode 'A' + i
    row i = fromCharArray $ mirror $ row' i
    row' i = replicate (n - i) ' ' <> [char i] <> replicate i ' '
    mirror ∷ ∀ a. Array a → Array a
    mirror xs = xs <> (drop 1 $ reverse $ xs)

What can you learn from this solution?

A huge amount can be learned from reading other people’s code. This is why we wanted to give exercism users the option of making their solutions public.

Here are some questions to help you reflect on this solution and learn the most from it.

  • What compromises have been made?
  • Are there new concepts here that you could read more about to improve your understanding?