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BadChicken's solution

to Crypto Square in the Clojure Track

Published at Apr 04 2021 · 0 comments
Test suite

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:


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:

"sroots  "

The coded message is obtained by reading down the columns going left to right.

The message above is coded as:


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:

"aohghn "
"sseoau "


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

Submitting Incomplete Solutions

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(ns crypto-square-test
  (:require [clojure.test :refer [deftest is]]

(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 :refer [lower-case trim join]]
            [clojure.math.numeric-tower :refer [sqrt ceil]]))

(defn- pad-right [size txt]
  (format (str "%-" size "s") txt))

(defn- pad-segments [size segments]
  (map (partial pad-right size) segments))

(defn- transpose-row
  "Each item in row is conj'd onto the corresponding row in coll."
  [coll row]
  (map #(conj %1 %2) coll row))

(defn- transpose-matrix [m]
  (let [n (count (first m))
        m (pad-segments n m)
        m' (repeat n [])]
    (->> m
         (reduce transpose-row m')
         (map #(apply str %)))))

(defn normalize-plaintext [txt]
  (->> txt
      (filter #(or (Character/isLetter %) (Character/isDigit %)))
      (apply str)))

(defn square-size [normalized-txt]
  (->> normalized-txt

(defn plaintext-segments [txt]
  (let [t (normalize-plaintext txt)
        c (square-size t)]
    (->> t
         (partition-all c)
         (map #(apply str %)))))

(defn- ciphertext-segments [txt]
  (let [segments (plaintext-segments txt)]
    (->> segments
         (map trim))))

(defn ciphertext [txt]
  (join (ciphertext-segments txt)))

(defn normalize-ciphertext [txt]
  (join " " (ciphertext-segments txt)))

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