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fredericcassin's solution

to Crypto Square in the Clojure Track

Published at May 17 2020 · 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 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 "

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_test.clj

(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 (:require [clojure.string :as str]))

(defn normalize-plaintext [t]
  (->> t (str/lower-case) (re-seq #"[a-z0-9]") (apply str)))

(defn square-size [t]
  (int (Math/ceil (Math/sqrt (count (normalize-plaintext t))))))

(defn plaintext-segments [t & f]
  (let [nt (normalize-plaintext t)
        cols (square-size nt)]
    (->> nt
         (partition cols cols (take cols (repeat \space)))
         (mapv #((if (nil? f) str/trim (first f)) (apply str %1))))))

(defn ciphertext [t]
  (->> (plaintext-segments t identity)
       (map seq)
       (apply map #(str/trim (apply str %&)))
       (apply str)))

(defn normalize-ciphertext [t & f]
  (let [nt (ciphertext t)
        count-all (int (Math/ceil (Math/sqrt (count nt))))
        cols (int (Math/round (Math/sqrt (count nt))))
        count-full-or-0 (int (mod (count nt) count-all))
        count-full (if (zero? count-full-or-0) count-all count-full-or-0) 
        [nt1 nt2] (split-at (* cols count-full) nt)]
    (->> (concat
          (partition cols nt1)
          (partition (dec cols) nt2))
         (mapv #((if (nil? f) str/trim (first f)) (apply str %1)))
         (str/join " "))))

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