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Published at Jan 29 2021
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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 "
```

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.

```
(ns crypto-square-test
(:require [clojure.test :refer [deftest is]]
crypto-square))
(deftest normalize-splunk
(is (= "splunk" (crypto-square/normalize-plaintext "s#!@$%plunk"))))
(deftest normalize-with-punctuation
(is (= "123go" (crypto-square/normalize-plaintext "1, 2, 3 GO!"))))
(deftest square-2
(is (= 2 (crypto-square/square-size "1234"))))
(deftest square-3
(is (= 3 (crypto-square/square-size "123456789"))))
(deftest square-4
(is (= 4 (crypto-square/square-size "123456789abc"))))
(deftest segments
(is (= ["neverv", "exthin", "eheart", "withid", "lewoes"]
(crypto-square/plaintext-segments "Never vex thine heart with idle woes."))))
(deftest segments-2
(is (= ["zomg", "zomb", "ies"]
(crypto-square/plaintext-segments "ZOMG! ZOMBIES!!!"))))
(deftest cipher-1
(is (= "tasneyinicdsmiohooelntuillibsuuml"
(crypto-square/ciphertext "Time is an illusion. Lunchtime doubly so."))))
(deftest cipher-2
(is (= "wneiaweoreneawssciliprerlneoidktcms"
(crypto-square/ciphertext "We all know interspecies romance is weird."))))
(deftest cipher-3
(is (= "msemo aanin dnin ndla etlt shui"
(crypto-square/normalize-ciphertext "Madness, and then illumination."))))
(deftest cipher-4
(is (= "vrel aepe mset paoo irpo"
(crypto-square/normalize-ciphertext "Vampires are people too!"))))
(deftest cipher-5
(is (= (str "ageihdsednsh lsagtoonaepe lannswnccair hrditeaetnrh "
"ueethdnatoio mbqyewdnotto aouayicdwhod nranatosaef "
"bnldrhnhrrb efirersodir irnieecusno nedgnailoat")
(let [plaintext (str "All human beings are born free "
"and equal in dignity and rights. "
"They are endowed with reason and conscience "
"and should act towards one another "
"in a spirit of brotherhood.")]
(crypto-square/normalize-ciphertext plaintext)))))
```

```
(ns crypto-square)
(defn letter? [c] (Character/isLetter c))
(defn digit? [c] (Character/isDigit c))
(defn not-space? [c] (not= \space c))
(defn normalize-plaintext [s]
(->> s
(filter #(or (letter? %) (digit? %)))
(apply str)
(clojure.string/lower-case)))
(defn square-size [s]
(let [length (count s)
candidate-size (int (Math/sqrt length))
r (quot length candidate-size)
c (quot length r)]
(if (or (< c r) (< (* c r) length))
(inc candidate-size)
candidate-size)))
(defn plaintext-segments
([s] (plaintext-segments s true))
([s trim?]
(let [s (normalize-plaintext s)
size (square-size s)]
(->>
(partition size size (repeat \space) s)
(filter (if trim? not-space? identity))
(map (fn [chars] (apply str (if trim?
(filter not-space? chars)
chars))))
(filter seq)))))
(defn ciphertext
([s] (ciphertext s false))
([s keep-space?]
(->> (plaintext-segments s false)
(apply interleave)
(filter (if keep-space? identity not-space?))
(apply str))))
(defn normalize-ciphertext [s]
(let [s (ciphertext s true)
c (square-size s)
r (quot (count s) c)]
(->> (partition r s)
(map #(apply str (if (= \space (last %))
(butlast %)
%)))
(clojure.string/join " "))))
```

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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