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:
The plaintext should be organized in to a rectangle. The size of the
r x c) should be decided by the length of the message,
c >= r and
c - r <= 1, where
c is the number of columns
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:
Output the encoded text in chunks that fill perfect rectangles
(r X c),
c chunks of
r length, separated by spaces. For phrases that are
n characters short of the perfect rectangle, pad each of the last
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:
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
# frozen_string_literal: true class Crypto SPACES_AND_PUNCTUATION = /[[[:space:]][[:punct:]]]/.freeze private_constant :SPACES_AND_PUNCTUATION def initialize(plaintext) @plaintext = plaintext end def ciphertext return plaintext if plaintext.empty? encode(rectangle) end private attr_reader :plaintext def rectangle collection = normalised_plaintext.chars padding = (columns - collection.length % columns) % columns collection.concat(Array.new(padding, " ")).each_slice(columns).to_a end def normalised_plaintext @normalised_plaintext ||= plaintext.downcase.strip.gsub(SPACES_AND_PUNCTUATION, "") end def columns @columns ||= Math.sqrt(normalised_plaintext.length).ceil end def encode(rectangle) rectangle.transpose.map(&:join).join(" ") end end
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.