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SergiiVlasiuk's solution

to Crypto Square in the Scala Track

Published at Aug 25 2019 · 0 comments
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. Phrases that fill perfect rectangles (r X c) should be output c chunks of r length, separated by spaces. Phrases that do not fill perfect rectangles will have n empty spaces. Those spaces should be distributed evenly, added to the end of the last n chunks.

imtgdvs fearwer mayoogo anouuio ntnnlvt wttddes aohghn  sseoau 

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

imtgdvs
fearwer
mayoogo
anouuio
ntnnlvt
wttddes
aohghn
sseoau

The Scala exercises assume an SBT project scheme. The exercise solution source should be placed within the exercise directory/src/main/scala. The exercise unit tests can be found within the exercise directory/src/test/scala.

To run the tests simply run the command sbt test in the exercise directory.

For more detailed info about the Scala track see the help page.

Source

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

Submitting Incomplete Solutions

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

CryptoSquareTest.scala

import org.scalatest.{Matchers, FunSuite}

/** @version 3.2.0 */
class CryptoSquareTest extends FunSuite with Matchers {

  test("empty plaintext results in an empty ciphertext") {
    CryptoSquare.ciphertext("") should be("")
  }

  test("Lowercase") {
    pending
    CryptoSquare.ciphertext("A") should be("a")
  }

  test("Remove spaces") {
    pending
    CryptoSquare.ciphertext("  b ") should be("b")
  }

  test("Remove punctuation") {
    pending
    CryptoSquare.ciphertext("@1,%!") should be("1")
  }

  test("9 character plaintext results in 3 chunks of 3 characters") {
    pending
    CryptoSquare.ciphertext("This is fun!") should be("tsf hiu isn")
  }

  test(
    "8 character plaintext results in 3 chunks, the last one with a trailing space") {
    pending
    CryptoSquare.ciphertext("Chill out.") should be("clu hlt io ")
  }

  test(
    "54 character plaintext results in 7 chunks, the last two with trailing spaces") {
    pending
    CryptoSquare.ciphertext(
      "If man was meant to stay on the ground, god would have given us roots.") should be(
      "imtgdvs fearwer mayoogo anouuio ntnnlvt wttddes aohghn  sseoau ")
  }
}
object CryptoSquare {
  private def normalize(message: String): String = message.toLowerCase.replaceAll("[\\W]|_", "")

  private def numberRows(msgLength: Int): Int = Math.sqrt(msgLength).toInt

  def ciphertext(message: String): String = {
    if (message.isEmpty) ""
    else {
      val normalized = normalize(message)
      val numRows = numberRows(normalized.length)
      val numCols = if ((numRows * numRows) % normalized.length > 0) numRows + 1 else numRows
      val chunks: List[String] = normalized.sliding(numCols, numCols).toList.map(f => f.padTo(numCols, " ").mkString)
      (0 until numCols).map(idx => chunks.map(_ (idx))).toList.map(_.mkString).mkString(" ")
    }
  }
}

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