 # jimweirich's solution

## to Crypto Square in the Clojure Track

Published at Jul 13 2018 · 2 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 cyphertext 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"
(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)))))``````
``````(require '[clojure.string :as str])

(defn- char-range
"Define a range of characters (inclusive)."
[start stop]
(map char (range (int start) (inc (int stop)))))

(def digits (char-range \0 \9))
(def alphabet (char-range \a \z))

(def valid-chararacters
(-> #{} (into digits) (into alphabet)))

;;; Utility functions

(defn- stringify
"Convert a sequence into a string."
[sequence]
(apply str sequence))

(defn- groups-of
"Group the sequence into chunks of size (last group may be short)."
[size s]
(if (empty? s) []
(loop [result []  s s]
tail (drop size s)
(if (empty? tail) new-result
(recur new-result tail))))))

(defn- spaced-groups-of
"Introduce spaces at size intervals."
[size string]
(->> string
(groups-of size)
(map stringify)
(str/join " ")))

(defn- remove-spaces
"Remove spaces from a string."
[string]
(filter #(not= \space %) string))

(defn make-size
"Return a function that appends spaces to a group so that it is at size."
[size]
(fn [s]
(if (= size (count s)) s
(into (vec s) (take (- size (count s)) (cycle " "))))))

(defn- ensure-sized-groups
"Ensure all groups are at least size in length."
[size groups]
(map (make-size size) groups))

(defn- normalize-group-lengths
"Pad any short groups to the max length."
[groups]
(if (empty? groups) []
(let [size (apply max (map count groups))]
(ensure-sized-groups size groups))))

(defn- stringify-groups
"Join all groups into a single character string."
[groups]
(->> groups
(map stringify)
stringify))

(defn- remove-spaces-from-groups
"Remove any spaces from the grouped sequences."
[groups]
(map remove-spaces groups))

(defn- transpose-equal-sized-groups
"Same as tranaspose, but only works with equal sized groups."
[groups]
(apply map (cons str groups)))

(defn- transpose
"Transpose a group of sequences, resulting in another group of sequences."
[groups]
(->> groups
normalize-group-lengths
transpose-equal-sized-groups
remove-spaces-from-groups))

(defn size-bigger-than-square
"Return a predicate function that is true when size is bigger than
the square of its input."
[size]
(fn [n] (> size (* n n))))

;;; Public functions

(defn square-size
"Determine the size of the square needed to encode a normalized string."
[normalized-string]
(let [size (count normalized-string)]
(first (drop-while (size-bigger-than-square size)
(iterate inc 1)))))

(defn normalize-plaintext
"Normalize the plaintext by removing non-alphanumeric characters."
[string]
(->> string
(str/lower-case)
(filter valid-chararacters)
stringify))

(defn plaintext-segments
"Break a normalized string into appropriate sized segments."
[string]
(let [normal (normalize-plaintext string)
size (square-size normal)]
(->> normal
(groups-of size)
(map stringify))))

(defn ciphertext
"Generate a non-grouped string of encoded text."
[string]
(->> string
plaintext-segments
transpose
stringify-groups))

(defn normalize-ciphertext
[string]
(->> string
ciphertext
(spaced-groups-of 5)))`````` jimweirich
Solution Author
commented over 7 years ago

Renamed parameter to spaced-groups-of to make it clear it gets a string (or at least a sequence of characters). Unless you wanted to implement some Clojure functions yourself, you might want to have a look at the following:

line 21: partition, partition-all line 32: partition, interpose line 40: clojure.string/trim line 97: Math/ceil, Math/sqrt line 109: clojure.string/replace #"\W" ""

Also, I'm not sure whether your usage of higher-order-functions (lines 48, 93) makes things more understandable.

### What can you learn from this solution?

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