Avatar of brunnock

brunnock's solution

to Crypto Square in the JavaScript 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.

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

Setup

Go through the setup instructions for JavaScript to install the necessary dependencies:

http://exercism.io/languages/javascript/installation

Running the test suite

The provided test suite uses Jasmine. You can install it by opening a terminal window and running the following command:

npm install -g jasmine

Run the test suite from the exercise directory with:

jasmine crypto-square.spec.js

In many test suites all but the first test have been marked "pending". Once you get a test passing, activate the next one by changing xit to it.

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.

crypto-square.spec.js

var Crypto = require('./crypto-square');

describe('Crypto', function () {
  it('normalize strange characters', function () {
    var crypto = new Crypto('s#$%^&plunk');
    expect(crypto.normalizePlaintext()).toEqual('splunk');
  });

  xit('normalize numbers', function () {
    var crypto = new Crypto('1, 2, 3 GO!');
    expect(crypto.normalizePlaintext()).toEqual('123go');
  });

  xit('size of small square', function () {
    var crypto = new Crypto('1234');
    expect(crypto.size()).toEqual(2);
  });

  xit('size of small square with additional non-nuber chars', function () {
    var crypto = new Crypto('1 2 3 4');
    expect(crypto.size()).toEqual(2);
  });

  xit('size of slightly larger square', function () {
    var crypto = new Crypto('123456789');
    expect(crypto.size()).toEqual(3);
  });

  xit('size of non-perfect square', function () {
    var crypto = new Crypto('123456789abc');
    expect(crypto.size()).toEqual(4);
  });

  xit('plain text segments', function () {
    var crypto = new Crypto('Never vex thine heart with idle woes');
    expect(crypto.plaintextSegments()).toEqual(['neverv', 'exthin', 'eheart', 'withid', 'lewoes']);
  });

  xit('plain text segments', function () {
    var crypto = new Crypto('ZOMG! ZOMBIES!!!');
    expect(crypto.plaintextSegments()).toEqual(['zomg', 'zomb', 'ies']);
  });

  xit('cipher text', function () {
    var crypto = new Crypto('Time is an illusion. Lunchtime doubly so.');
    expect(crypto.ciphertext()).toEqual('tasneyinicdsmiohooelntuillibsuuml');
  });

  xit('cipher text', function () {
    var crypto = new Crypto('We all know interspecies romance is weird.');
    expect(crypto.ciphertext()).toEqual('wneiaweoreneawssciliprerlneoidktcms');
  });
});
var Crypto = function(message) {
  this.normalizePlaintext = function () {
    return message = message.replace(/\W/g,'').toLowerCase();
  }

  this.size = function() {
    return Math.ceil(Math.sqrt(message.length));
  }

  this.plaintextSegments = function() {
    this.normalizePlaintext();
    return message.match(this.splitRegEx());
  }

  this.ciphertext = function() {
    var plain = this.plaintextSegments();
    var code='';
    for (var y=0; y<this.size(); ++y) {
      for (var x=0; x<plain.length; ++x) {
	code += plain[x].slice(y,y+1);
      }
    }
    return code;
  }

  this.normalizeCiphertext = function() {
    return this.ciphertext().match(this.splitRegEx()).join(' ');
  }

  this.splitRegEx = function(){ 
    return new RegExp('.{1,' + this.size() + '}' ,'g');
  }
}

module.exports=Crypto;

Community comments

Find this solution interesting? Ask the author a question to learn more.

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?