Published at May 03 2019
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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 "
```

To run the tests, run the command `dotnet test`

from within the exercise directory.

Initially, only the first test will be enabled. This is to encourage you to solve the exercise one step at a time.
Once you get the first test passing, remove the `Skip`

property from the next test and work on getting that test passing.
Once none of the tests are skipped and they are all passing, you can submit your solution
using `exercism submit CryptoSquare.cs`

For more detailed information about the C# track, including how to get help if you're having trouble, please visit the exercism.io C# language page.

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

```
// This file was auto-generated based on version 3.2.0 of the canonical data.
using Xunit;
public class CryptoSquareTest
{
[Fact]
public void Empty_plaintext_results_in_an_empty_ciphertext()
{
var plaintext = "";
var expected = "";
Assert.Equal(expected, CryptoSquare.Ciphertext(plaintext));
}
[Fact(Skip = "Remove to run test")]
public void Lowercase()
{
var plaintext = "A";
var expected = "a";
Assert.Equal(expected, CryptoSquare.Ciphertext(plaintext));
}
[Fact(Skip = "Remove to run test")]
public void Remove_spaces()
{
var plaintext = " b ";
var expected = "b";
Assert.Equal(expected, CryptoSquare.Ciphertext(plaintext));
}
[Fact(Skip = "Remove to run test")]
public void Remove_punctuation()
{
var plaintext = "@1,%!";
var expected = "1";
Assert.Equal(expected, CryptoSquare.Ciphertext(plaintext));
}
[Fact(Skip = "Remove to run test")]
public void Number_9_character_plaintext_results_in_3_chunks_of_3_characters()
{
var plaintext = "This is fun!";
var expected = "tsf hiu isn";
Assert.Equal(expected, CryptoSquare.Ciphertext(plaintext));
}
[Fact(Skip = "Remove to run test")]
public void Number_8_character_plaintext_results_in_3_chunks_the_last_one_with_a_trailing_space()
{
var plaintext = "Chill out.";
var expected = "clu hlt io ";
Assert.Equal(expected, CryptoSquare.Ciphertext(plaintext));
}
[Fact(Skip = "Remove to run test")]
public void Number_54_character_plaintext_results_in_7_chunks_the_last_two_with_trailing_spaces()
{
var plaintext = "If man was meant to stay on the ground, god would have given us roots.";
var expected = "imtgdvs fearwer mayoogo anouuio ntnnlvt wttddes aohghn sseoau ";
Assert.Equal(expected, CryptoSquare.Ciphertext(plaintext));
}
}
```

```
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;
public static class CryptoSquare
{
private static readonly Regex regex = new Regex("\\W");
public static string NormalizedPlaintext(string plaintext) =>
regex.Replace(plaintext.ToLower(), "");
public static IEnumerable<string> PlaintextSegments(string plaintext)
{
var normalized = NormalizedPlaintext(plaintext);
var size = GetRectangleSize(normalized.Length);
normalized += new string(' ', size.Item2);
var rectangle = new string[size.Item1];
for (int i = 0; i < rectangle.Length; i++)
{
rectangle[i] = normalized.Substring(i * size.Item2, size.Item2);
}
return rectangle;
}
public static string Encoded(string plaintext)
{
var segments = PlaintextSegments(plaintext).ToArray();
if (segments.Length == 0)
{
return "";
}
var result = "";
for (int i = 0; i < segments[0].Length; i++)
{
for (int j = 0; j < segments.Length; j++)
{
if (segments[j][i] != ' ')
{
result += segments[j][i];
}
}
}
return result;
}
public static string Ciphertext(string plaintext)
{
var encoded = Encoded(plaintext);
var size = GetRectangleSize(encoded.Length);
var few = size.Item1 * size.Item2 - encoded.Length;
var rectangle = new string[size.Item2];
for (int i = 0; i < rectangle.Length - few; i++)
{
rectangle[i] = encoded.Substring(i * size.Item1, size.Item1);
}
for (int i = 0; i < few; i++)
{
rectangle[rectangle.Length - few + i] = encoded.Substring((rectangle.Length - few + i) * size.Item1 - i, size.Item1 - 1) + " ";
}
return string.Join(" ", rectangle);
}
private static (int, int) GetRectangleSize(int lenght)
{
var sqrt = (int)Math.Sqrt(lenght);
return sqrt * sqrt == lenght
? (sqrt, sqrt)
: lenght <= sqrt * (sqrt + 1)
? (sqrt, sqrt + 1)
: (sqrt + 1, sqrt + 1);
}
}
```

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?

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