# Eggman's solution

## to Diamond in the Ruby Track

Published at Aug 07 2020 · 0 comments
Instructions
Test suite
Solution

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 `路` characters.

Diamond for letter 'A':

``````A
``````

Diamond for letter 'C':

``````路路A路路

C路路路C

``````

Diamond for letter 'E':

``````路路路路A路路路路

E路路路路路路路E

``````

For installation and learning resources, refer to the Ruby resources page.

For running the tests provided, you will need the Minitest gem. Open a terminal window and run the following command to install minitest:

``````gem install minitest
``````

If you would like color output, you can `require 'minitest/pride'` in the test file, or note the alternative instruction, below, for running the test file.

Run the tests from the exercise directory using the following command:

``````ruby diamond_test.rb
``````

To include color from the command line:

``````ruby -r minitest/pride diamond_test.rb
``````

## Submitting Incomplete Solutions

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

### diamond_test.rb

``````require 'minitest/autorun'
require_relative 'diamond'

class DiamondTest < Minitest::Test
def test_letter_a
end

def test_letter_c
skip
string = "  A  \n"\
" B B \n"\
"C   C\n"\
" B B \n"\
"  A  \n"
end

def test_letter_e
skip
string = "    A    \n"\
"   B B   \n"\
"  C   C  \n"\
" D     D \n"\
"E       E\n"\
" D     D \n"\
"  C   C  \n"\
"   B B   \n"\
"    A    \n"
end
end``````
``````module Diamond

private

def self.units_between(letter)
(letter.ord - "B".ord) * 2 + 1
end

def self.row_width(letter)
2 + units_between(letter)
end

def self.units_outside(letter, max_width)
(max_width - 2 - units_between(letter)) / 2
end

def self.row(letter, max_width)
format_row(
letter,
units_between(letter),
units_outside(letter, max_width),
max_width
)
end

def self.format_row(letter, inners, outers, max_width)
letter == "A" ?
"#{' ' * ((max_width - 1) / 2)}A#{' ' * ((max_width - 1) / 2)}\n" :
"#{' ' * outers}#{letter}#{' ' * inners}#{letter}#{' ' * outers}\n"
end

public

def self.make_diamond(letter)
top = ("A"...letter).map { |l| row(l, row_width(letter)) }
middle = [format_row(letter, units_between(letter), 0, row_width(letter))]
bottom = top.reverse
( top + middle + bottom ).join
end

end``````