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Published at Apr 13 2020
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Instructions

Test suite

Solution

Implement the classic method for composing secret messages called a square code.

Given an English text, output the encoded version of that text.

First, the input is normalized: the spaces and punctuation are removed from the English text and the message is downcased.

Then, the normalized characters are broken into rows. These rows can be regarded as forming a rectangle when printed with intervening newlines.

For example, the sentence

```
"If man was meant to stay on the ground, god would have given us roots."
```

is normalized to:

```
"ifmanwasmeanttostayonthegroundgodwouldhavegivenusroots"
```

The plaintext should be organized in to a rectangle. The size of the
rectangle (`r x c`

) should be decided by the length of the message,
such that `c >= r`

and `c - r <= 1`

, where `c`

is the number of columns
and `r`

is the number of rows.

Our normalized text is 54 characters long, dictating a rectangle with
`c = 8`

and `r = 7`

:

```
"ifmanwas"
"meanttos"
"tayonthe"
"groundgo"
"dwouldha"
"vegivenu"
"sroots "
```

The coded message is obtained by reading down the columns going left to right.

The message above is coded as:

```
"imtgdvsfearwermayoogoanouuiontnnlvtwttddesaohghnsseoau"
```

Output the encoded text in chunks that fill perfect rectangles `(r X c)`

,
with `c`

chunks of `r`

length, separated by spaces. For phrases that are
`n`

characters short of the perfect rectangle, pad each of the last `n`

chunks with a single trailing space.

```
"imtgdvs fearwer mayoogo anouuio ntnnlvt wttddes aohghn sseoau "
```

Notice that were we to stack these, we could visually decode the ciphertext back in to the original message:

```
"imtgdvs"
"fearwer"
"mayoogo"
"anouuio"
"ntnnlvt"
"wttddes"
"aohghn "
"sseoau "
```

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 crypto_square_test.rb
```

To include color from the command line:

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

J Dalbey's Programming Practice problems http://users.csc.calpoly.edu/~jdalbey/103/Projects/ProgrammingPractice.html

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

```
require 'minitest/autorun'
require_relative 'crypto_square'
# Common test data version: 3.2.0 e00dfb3
class CryptoSquareTest < Minitest::Test
def test_empty_plaintext_results_in_an_empty_ciphertext
# skip
plaintext = ''
assert_equal "", Crypto.new(plaintext).ciphertext
end
def test_lowercase
skip
plaintext = 'A'
assert_equal "a", Crypto.new(plaintext).ciphertext
end
def test_remove_spaces
skip
plaintext = ' b '
assert_equal "b", Crypto.new(plaintext).ciphertext
end
def test_remove_punctuation
skip
plaintext = '@1,%!'
assert_equal "1", Crypto.new(plaintext).ciphertext
end
def test_9_character_plaintext_results_in_3_chunks_of_3_characters
skip
plaintext = 'This is fun!'
assert_equal "tsf hiu isn", Crypto.new(plaintext).ciphertext
end
def test_8_character_plaintext_results_in_3_chunks_the_last_one_with_a_trailing_space
skip
plaintext = 'Chill out.'
assert_equal "clu hlt io ", Crypto.new(plaintext).ciphertext
end
def test_54_character_plaintext_results_in_7_chunks_the_last_two_with_trailing_spaces
skip
plaintext = 'If man was meant to stay on the ground, god would have given us roots.'
assert_equal "imtgdvs fearwer mayoogo anouuio ntnnlvt wttddes aohghn sseoau ", Crypto.new(plaintext).ciphertext
end
end
```

```
# Crypto
#
class Crypto
def initialize(plaintext)
@plaintext = normalize_text(plaintext)
end
def ciphertext
return '' if @plaintext.empty?
(width, height) = calculate_size
matrix = fill_matrix(height)
output = transpose_matrix(matrix, width)
remove_extra_whitespace(output)
end
private
def fill_matrix(height)
matrix = []
@plaintext.chars.each_slice(height) do |slice|
matrix << slice.fill(' ', slice.length, height - slice.length)
end
matrix
end
def transpose_matrix(matrix, width)
output = []
matrix.transpose.flatten.each_slice(width) do |slice|
output << slice.join
output << ' '
end
output
end
def remove_extra_whitespace(output)
output[0..-2].join
end
def normalize_text(text)
text.gsub(/ |,|\@|\?|\!|\%|\./, '').downcase
end
def calculate_size
length = @plaintext.length
width = Math.sqrt(length).floor
height = Math.sqrt(length).ceil
width += 1 unless width * height >= length
[width, height]
end
end
```

A huge amount can be learned from reading other peopleâ€™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?

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