Add crypto-square exercise (#75)

* Add crypto-square exercise

Implement tests and example solution
Generate README
Update config

config.json

@@ -323,6 +323,19 @@
       "unlocked_by": "sum-of-multiples",
       "uuid": "2f7b585f-f82f-4dca-9588-2df3250184e6"
     },
+    {
+      "uuid": "82c43534-86ff-4b5a-9519-1501a15721bf",
+      "slug": "crypto-square",
+      "core": false,
+      "unlocked_by": "rotational-cipher",
+      "difficulty": 4,
+      "topics": [
+        "strings",
+        "text_formatting",
+        "regular_expressions",
+        "transforming"
+      ]
+    },
     {
       "uuid": "7cad82d6-0db6-d680-4133-81d850d6e7a925454a0",
       "slug": "diamond",

exercises/crypto-square/README.md

@@ -0,0 +1,84 @@
+# Crypto Square
+
+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`:
+
+```plain
+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:
+
+```plain
+imtgdvsfearwermayoogoanouuiontnnlvtwttddesaohghnsseoau
+```
+
+Output the encoded text in chunks.  Phrases that fill perfect squares
+`(r X r)` should be output in `r`-length chunks separated by spaces.
+Imperfect squares will have `n` empty spaces.  Those spaces should be distributed evenly across the last `n` rows.
+
+```plain
+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:
+
+```plain
+imtgdvs
+fearwer
+mayoogo
+anouuio
+ntnnlvt
+wttddes
+aohghn
+sseoau
+```
+
+## Installation
+See [this guide](https://github.com/exercism/xr/blob/master/docs/INSTALLATION.md) for instructions on how to setup your local R environment.
+
+## How to implement your solution
+In each problem folder, there is a file named `<exercise_name>.R` containing a function that returns a `NULL` value. Place your implementation inside the body of the function.
+
+## How to run tests
+Inside of RStudio, simply execute the `test_<exercise_name>.R` script. This can be conveniently done with [testthat's `auto_test` function](https://www.rdocumentation.org/packages/testthat/topics/auto_test). Because exercism code and tests are in the same folder, use this same path for both  `code_path` and `test_path` parameters. On the command-line, you can also run `Rscript test_<exercise_name>.R`.
+
+## Source
+
+J Dalbey's Programming Practice problems [http://users.csc.calpoly.edu/~jdalbey/103/Projects/ProgrammingPractice.html](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.

exercises/crypto-square/crypto-square.R

@@ -0,0 +1,15 @@
+normalized_plaintext <- function(input) {
+
+}
+
+plaintext_segments <- function(input) {
+
+}
+
+encoded <- function(input) {
+
+}
+
+ciphertext <- function(input) {
+
+}

exercises/crypto-square/example.R

@@ -0,0 +1,47 @@
+library(magrittr)
+
+normalized_plaintext <- function(input) {
+
+  gsub("[^[:alnum:]]", "", input) %>% 
+    tolower()
+
+}
+
+map_plaintext_to_matrix <- function(input) {
+
+  txt <- normalized_plaintext(input)
+  width <- max(1, nchar(txt) %>% sqrt() %>% ceiling())
+  ext_len <- ceiling(nchar(txt) / width) * width
+  txt <- sprintf(paste0("%-", ext_len, "s"), txt)
+
+  strsplit(txt, "") %>% 
+    unlist() %>% 
+    matrix(ncol = width, byrow = TRUE)
+
+}
+
+plaintext_segments <- function(input) {
+
+  if (!nzchar(input)) return("")
+  map_plaintext_to_matrix(input) %>% 
+    apply(MARGIN = 1, paste, collapse = "") %>% 
+    trimws()
+
+}
+
+encoded <- function(input) {
+
+  map_plaintext_to_matrix(input) %>% 
+    apply(MARGIN = 2, paste, collapse = "") %>% 
+    trimws() %>% 
+    paste(collapse = "")
+
+}
+
+ciphertext <- function(input) {
+
+  map_plaintext_to_matrix(input) %>%   
+    apply(MARGIN = 2, paste, collapse = "") %>% 
+    paste(collapse = " ")
+
+}

exercises/crypto-square/test_crypto-square.R

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+source("./crypto-square.R")
+library(testthat)
+
+test_that("Lowercase", {
+  expect_equal(normalized_plaintext("Hello"), "hello")
+})
+
+test_that("Remove spaces", {
+  expect_equal(normalized_plaintext("Hi there"), "hithere")
+})
+
+test_that("Remove punctuation", {
+  expect_equal(normalized_plaintext("@1, 2%, 3 Go!"), "123go")
+})
+
+test_that("empty plaintext results in an empty rectangle", {
+  expect_equal(plaintext_segments(""), "")
+})
+
+test_that("4 character plaintext results in an 2x2 rectangle", {
+  expect_equal(plaintext_segments("Ab Cd"), c("ab", "cd"))
+})
+
+test_that("9 character plaintext results in an 3x3 rectangle", {
+  expect_equal(plaintext_segments("This is fun!"), c("thi", "sis", "fun"))
+})
+
+test_that("54 character plaintext results in an 8x7 rectangle", {
+  expect_equal(plaintext_segments(
+    "If man was meant to stay on the ground, god would have given us roots."), 
+    c("ifmanwas",
+      "meanttos",
+      "tayonthe",
+      "groundgo",
+      "dwouldha",
+      "vegivenu",
+      "sroots"))
+})
+
+test_that("empty plaintext results in an empty encode", {
+  expect_equal(encoded(""), "")
+})
+
+test_that("Non-empty plaintext results in the combined plaintext segments", {
+  expect_equal(encoded(
+    "If man was meant to stay on the ground, god would have given us roots."), 
+    "imtgdvsfearwermayoogoanouuiontnnlvtwttddesaohghnsseoau")
+})
+
+test_that("empty plaintext results in an empty ciphertext", {
+  expect_equal(ciphertext(""), "")
+})
+
+test_that("9 character plaintext results in 3 chunks of 3 characters", {
+  expect_equal(ciphertext("This is fun!"), "tsf hiu isn")
+})
+
+test_that("54 character plaintext results in 7 chunks, the last two padded with 
+          spaces", {
+  expect_equal(ciphertext(
+    "If man was meant to stay on the ground, god would have given us roots."), 
+    "imtgdvs fearwer mayoogo anouuio ntnnlvt wttddes aohghn  sseoau ")
+})
+
+message("All tests passed for exercise: crypto-square")